Composite particles

ABSTRACT

A coating containing pigment particles and a polymer matrix is provided. The coating contains pigment particles that have a scattering coefficient with a linear or quasi-linear relationship to the pigment volume concentration of those pigment particles. The coating has improved hiding and is useful as a protective coating or an aesthetic coating on an underlying substrate. Also provided are compositions useful for preparing the coating, including covalently bonded composite particles and aqueous dispersions containing composite particles. The composite particles each contain a pigment particle with a plurality of polymer particles attached by adsorption on the outer surface of the pigment particle or by covalent bonding to the pigment particle through a coupling agent. Methods to prepare the composite particles and coating compositions containing the composite particles are also provided.

FIELD OF THE INVENTION

This invention relates generally to a coating containing opacifyingpigment particles and a polymer matrix. More specifically, the inventionrelates to such a coating wherein the opacifying pigment particles havea light scattering coefficient with a linear or quasi-linearrelationship to the volume concentration of the particles. The inventionfurther relates to a coating wherein the opacifying pigment particlesare composite particles, which are inorganic-organic particlescontaining an opacifying pigment particle with at least one polymerparticle attached thereto. This invention still further relates tomethods of preparing composite particles, and to a method of preparingcoating compositions containing composite particles.

BACKGROUND OF THE INVENTION

Opacifying pigments provide whiteness, and opacity or “hiding”, toopacifying coatings, such as paints. These pigments are present in allcoatings that are designed to provide an opaque coating on andconcealingly cover an undersurface or substrate surface to which thecoating is applied. Opacifying pigments are absent from those coatingsthat are designed to be clear or transparent. Opacifying pigments arepresent in opacifying coatings, especially paints. In paints, theopacifying pigment is present irrespective of whether the paint is whiteor colored. The opacifying pigment of all paints is distinguished fromthe color specific pigments, also known as tinting agents or colorants,which are additionally present in colored paints. It is the colorspecific pigments that provide the specific color or tint to non-whitepaints.

It is desirable that opacifying coatings and paints have a highopacifying capacity so as to enable the coating or paint to completelyconceal the undersurface, even if of a sharply contrasting color, whileutilizing a minimal application of the coating or paint. It is highlydesirable that complete covering of the undersurface is attained with asingle application of the coating or paint, having the minimum possiblethickness.

Opacifying coating and paint manufacturers have long sought to formulateopacifying coatings and paints having the desired opacity by maximizingthe level of hiding for a defined level of opacifying pigment, in anattempt to approach the theoretical maximum hiding capability for aspecific opacifying pigment, while minimizing the amount of opacifyingpigment actually utilized.

The opacifying capacity or hiding power of an opacifying coating orpaint is a measure of the coating's ability to conceal a surface towhich the coating is applied. Opacifying capacity is a function of thespacing between the particles of opacifying pigment in the dried appliedcoating. Opacifying capacity of a coating is maximized when the lightscattering capability of the opacifying pigment is maximized. Maximumlight scattering efficiency occurs when the opacifying pigment particleshave a certain diameter and spacing, so that the light scatteringcapability of each particle does not interfere with the light scatteringcapability of its neighboring particles. This condition may occur incoatings containing sufficiently low levels of opacifying pigment suchthat the individual opacifying pigment particles are isolated from eachother. Coatings containing such low levels of opacifying pigment,however, do not provide sufficient whiteness and hiding at typical driedcoating thicknesses. Achieving the desired levels of hiding andwhiteness typically requires higher levels of opacifying pigment. Atthese higher levels, a statistical distribution of opacifying pigmentparticles occurs, which results in at least some of the opacifyingpigment particles being in such close proximity to one another thatthere is a loss of light scattering efficiency due to crowding of theopacifying pigment particles.

Increased hiding efficiency is obtained by reducing the crowding of theopacifying pigment particles and minimizing the formation of clusters ofopacifying pigment particles. One method uses polymer particlescontaining select chemical groups which promote adsorption to theopacifying pigment particle.

For example, U.S. Pat. No. 5,385,960 discloses an aqueous dispersion ofcomposite particles, the composite particles each including a pluralityof selected polymeric latex particles adsorbed to a titanium dioxideopacifying pigment particle. The selected polymeric latex particles havedihydrogen phosphate functional groups, which promote adsorption of theselected polymeric latex particles onto the surface of the titaniumdioxide particles.

Although these composite particles provide improved hiding, there isstill a need to increase the hiding efficiency provided by theopacifying pigment particles, and in particular, to obtain coatingswhich have hiding values at or near the maximum limit predicted by lightscattering theory.

Theoretical hiding efficiency refers to the maximum level of hiding thatmay be obtained from a defined concentration of pigment particles and ischaracterized by a linear relationship between the scatteringcoefficient for the coating and the pigment concentration.

Titanium dioxide (TiO₂) is the most common opacifying pigment utilizedin opacifying coatings and paints today. Accordingly, the presentinvention is described hereinafter in the context of the maximumopacifying capacity for titanium dioxide, which occurs at an optimumparticle diameter of from about 200 to about 280 nanometers (nm), andwhen the particles are spaced apart from each other at distances on theorder of a few particle diameters. It is to be understood, however, thatthe scope of the present invention is not limited to titanium dioxide asthe opacifying pigment.

Titanium dioxide is the opacifying pigment of choice of most coatingsmanufacturers, particularly paint manufacturers, to provide whiteness,and opacity or “hiding”, to the final dried coating. Titanium dioxideis, however, typically the most expensive raw material in a coatingformulation. Heretofore, a number of techniques for minimizing theamount of TiO₂, while maximizing the level of hiding provided a certainamount of TiO₂ have been employed, including: (1) using titanium dioxidethat has an optimal average particle size and particle size distributionfor light scattering; and (2) using titanium dioxide that is welldispersed.

SUMMARY OF THE INVENTION

The present invention provides opacifying coatings having hiding valuesat or near theoretical hiding efficiency. These coatings arecharacterized as having opacifying pigment particles that have lightscattering coefficients with linear or quasi-linear relationships totheir pigment volume concentrations. An advantage of the coatings of thepresent invention is that for a desired level of hiding, these coatingscontain lower levels of pigment and/or are applied at lower coat weightsthan coatings previously known in the art. The use of the coatings ofthe present invention enables the attainment of increased hiding levels.

According to a first aspect of the present invention, an opacifyingcoating is provided containing pigment particles having an averageparticle diameter of up to about 1 micron, a surface, and an index ofrefraction of at least 1.8; and a polymer matrix for at least partiallycontaining the pigment particles; the pigment particles having a lightscattering coefficient, S, described by the equation:S=AV(1−BV _(eff) ^(1/3))wherein: V is the pigment volume concentration of the pigment particlesand is in the range of about 5 to about 40; V_(eff) is the effectivepigment volume concentration of the pigment particles; A is a constantwith a value greater than 0; and B is a constant with a value in therange of from 0 to 0.15.

A second aspect of the present invention provides a composite particleincluding a pigment particle and a plurality of polymer particles, eachone of the polymer particles containing at least one reactedcomplementary functional group forming a covalent bond with the pigmentparticle.

A third aspect of the present invention provides a composite particleincluding a pigment particle, a first plurality of polymer particles;and a second plurality of reacted coupling agents, such that each one ofthe reacted coupling agents is covalently bonded to the pigment particleand to a corresponding one of the first plurality of polymer particles.

A fourth aspect of the present invention provides a coating compositionincluding a composite particle containing: a pigment particle, a firstplurality of polymer particles, and a second plurality of reactedcoupling agents, such that each one of the reacted coupling agents iscovalently bonded to the pigment particle and to a corresponding one ofthe first plurality of polymer particles; and a binder.

A fifth aspect of the present invention provides a method for preparinga composite particle, wherein the composite particle contain a pigmentparticle and a first plurality of polymer particles attached to thepigment particle, the method including the steps of: admixing thepigment particle and a second plurality of molecules of a couplingagent, wherein each molecule of the coupling agent contains a firstfunctional group for reacting with the pigment particle to form a firstcovalent bond therewith, and a second functional group for reacting witha complementary functional group to form a second covalent bond; forminga modified pigment particle by reacting or allowing to react the pigmentparticle and at least a portion of the first functional groups of thesecond plurality of molecules of the coupling agent, such that themodified pigment particle has a third plurality of molecules of thecoupling agent with reacted first functional groups, covalently bondedthereto; admixing the modified pigment particle and the first pluralityof polymer particles, each of the first plurality of polymer particlescontaining the complementary functional group; and forming the compositeparticle by reacting or allowing to react the second functional group ofthe third plurality of molecules of the coupling agent and thecomplementary functional group of the first plurality of polymerparticles, forming a covalent bond therebetween, such that at least oneof the first plurality of the polymer particles is covalently bonded toone of the third plurality of molecules of the coupling agent.

The second, third, fourth, and fifth aspects of this invention relate,respectively, to covalently bonded composite particles, a coatingcomposition containing the covalently bonded composite particles, and amethod of preparing the covalently bonded composite particles.

A sixth aspect of the present invention provides an aqueous polymerdispersion including polymer particles containing polymerized units ofphosphorus acid monomer, and having first phosphorus acid groups; and anaqueous medium; such that the aqueous polymer dispersion issubstantially free of water soluble polymer having second phosphorusacid groups.

According to a seventh aspect of the present invention, a compositeparticle dispersion is provided including composite particles, each ofwhich contains a pigment particle having a surface, and a plurality ofpolymer particles containing polymerized units of phosphorus acidmonomer, and having first phosphorus acid groups, wherein the pluralityof polymer particles are adsorbed on the surface of the pigmentparticle; and an aqueous medium; wherein the composite particledispersion is substantially free of water soluble polymer bearing secondphosphorus acid groups and having a molecular weight of at least 40,000.

The aqueous polymer dispersion of the sixth aspect is suitable forpreparing the composite particle composition of the seventh aspect.

An eighth aspect of the present invention provides a process for formingthe composite particle composition of the seventh aspect of theinvention. The process includes the steps of: preparing an aqueouscomposition including pigment particles and polymer particles havingfirst phosphorus acid groups; wherein the polymer particles containpolymerized units of phosphorus acid monomer; and the aqueouscomposition is substantially free of water soluble polymer bearingsecond phosphorus acid groups and having a molecular weight of at least40,000; and permitting the polymer particles to adsorb onto the pigmentparticles to form the composite particles.

In a ninth aspect of the present invention, a coating is providedincluding composite particles; wherein each of the composite particlescontains a pigment particle having a surface; and a plurality of polymerparticles containing polymerized units of a phosphorus acid monomer andhaving first phosphorus acid groups, the plurality of polymer particlesbeing adsorbed on the surface of the pigment particle; such that thecomposite particles are formed by admixing the pigment particles and theplurality of polymer particles in an aqueous medium; wherein the aqueousmedium is substantially free of water soluble polymer having secondphosphorus acid groups and a molecular weight of at least 40,000.

The sixth and seventh aspects of the present invention relate tocompositions having aqueous mediums substantially free of water solublepolymer having second phosphorus acid groups. The eighth aspect of thepresent invention relates to a process for preparing the composition ofthe seventh aspect of the present invention. The ninth aspect relates toa coating prepared from the composition of the seventh aspect.

A tenth aspect of the present invention provides a process for preparingan aqueous dispersion containing polymer particles containingpolymerized units of phosphorus acid monomer, the process including thesteps of: adding a phosphorus acid monomer to an aqueous reactionmedium; and polymerizing the phosphorus acid monomer at a pH of lessthan 2 to form the aqueous dispersion of the polymer particles.

An eleventh aspect of the present invention provides an aqueousdispersion including polymer particles that contain polymerized units ofphosphorus acid monomer; wherein the polymer particles are prepared bypolymerization of the phosphorus acid monomer in an aqueous reactionmedium having a pH of less than 2.

In a twelfth aspect of the present invention, an aqueous composition isprovided containing at least one composite particle that contains apigment particle having an surface; and a plurality of polymer particlescontaining units of a phosphorus acid monomer that has been polymerizedin an aqueous reaction medium having a pH of less than 2, and whereinthe plurality of polymer particles are adsorbed on the surface of thepigment particle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of light scattering coefficient for a species ofpigment, S, as a function of the pigment volume concentration, V. Theplot shows the relationship between light scattering coefficient and thepigment volume concentration for coatings having B values of 0, 0.1,0.15, 0.17, and 0.23.

DETAILED DESCRIPTION OF THE INVENTION

Glossary of Terms

As used herein, the term “(meth)acrylate” refers to either acrylate ormethacrylate and the term “(meth)acrylic” refers to either acrylic ormethacrylic.

“Glass transition temperature” or “T_(g)” as used herein, means thetemperature at or above which a glassy polymer undergoes segmentalmotion of the polymer chain. Glass transition temperatures of a polymerare estimated by the Fox equation [Bulletin of the American PhysicalSociety 1, 3 Page 123 (1956)], as follows:$\frac{1}{T_{g}} = {\frac{w_{1}}{T_{g{(1)}}} + \frac{w_{2}}{T_{g{(2)}}}}$For a copolymer, w₁ and w₂ are the weight fraction of the twoco-monomers, and T_(g(1)) and T_(g(2)) are the glass transitiontemperatures, in degrees Kelvin, of the two corresponding homopolymers.For polymers containing three or more monomers, additional terms(w_(n)/T_(g(n))) are added. Alternatively, the T_(g) of a polymer phaseis calculated by using the appropriate values for the glass transitiontemperatures of homopolymers, which are found, for example, in “PolymerHandbook”, edited by J. Brandrup and E. H. Immergut, IntersciencePublishers. The values of T_(g) reported herein are calculated based onthe Fox equation.

As used herein, the term “covalent bond” refers to a bond between twoatoms formed by sharing at least one pair of electrons and expresslyexcludes ionic bonds, hydrogen bonds, bonds formed by adsorptionincluding chemical adsorption and physical adsorption, bonds formed fromvan der Waals bonds, and dispersion forces.

As used herein, the term “phosphorus acid group” refers to a phosphorusoxo acid having a POH moiety in which the hydrogen atom is ionizable orto the salt of the phosphorus oxo acid. In its salt or basic form, thephosphorus acid group has a metal ion or an ammonium ion replacing atleast one acid proton. Examples of phosphorus acid groups include groupsformed from phosphinic acid, phosphonic acid, phosphoric acid,pyrophosphinic acid, pyrophosphoric acid, partial esters thereof, andsalts thereof.

First Aspect of the Invention

The coating of the present invention has an opacifying pigment containedin a polymer matrix. Optionally, the coating also contains one or moreof extender particles and secondary pigment particles. The opacifyingpigment is present as particles that are distributed within the polymermatrix. The opacifying pigment particles provide light scattering siteswithin the coating. The coating has at least one such opacifyingpigment, the particles of which have a scattering coefficient with alinear or quasi-linear relationship to the pigment volume concentrationof that pigment.

As used hereinafter, the terms “pigment”, “type of pigment”, “type ofpigment particles”, and “species of pigment particles” are used to referto the various embodiments of primary opacifying pigment and particlesthereof in the coating according to the present invention.

The shape of the pigment particles is not important and can be of anyshape provided that the pigment particles scatter photons havingwavelengths in the spectral region of from about 750 nm to about 300 nm,preferably in the visible spectral region of from about 700 nm to about380 nm. Suitable shapes for the pigment particles include sphericalshapes, such as a regular sphere, an oblate sphere, a prolate sphere,and an irregular sphere; cubic shapes such as a regular cube and arhombus; plate-like shapes including a flat plate, a concave plate, anda convex plate; and irregular shapes. The pigment particles havingspherical shapes preferably have average diameters in the range of fromabout 10 nm to about 1 micron, preferably in the range of from about 100nm to about 500 nm, and more preferably, in the range of from about 200nm to about 300 nm. Pigment particles having nonspherical shapespreferably have average diameters, defined as their maximum dimension,of up to about 1 micron, preferably up to about 500 nm, and morepreferably up to about 300 nm. Information about the average diametersof pigment particles is typically provided by pigment particlesuppliers.

The pigment particles are also characterized as having an index ofrefraction that is significantly greater than the index of refraction ofthe polymer matrix. Suitable pigment particles have an index ofrefraction of at least 1.8, preferably at least 1.9, and more preferablyat least 2.0. The indices of refraction for various materials are listedin CRC Handbook of Chemistry and Physics, 80^(th) Edition, D. R. Lide,editor, CRC Press, Boca Raton, Fla., 1999, pages 4-139 to 4-146.

The pigment particles alternatively have a uniform composition, or aheterogeneous composition with two or more phases. Certain heterogeneouspigment particles have an inner core and surrounding shell structurewherein one type of pigment particle forms the core and another type ofparticle forms the shell. The core and shell heterogeneous pigmentparticles include core/shell particles having a shell completely orincompletely encapsulating the core; core/shell particles having morethan one core; dipolar particles; and particles having multiple domainsof one phase on the surface of the other phase. Pigment particles, suchas titanium dioxide, can have at least one coating of one or more ofsilica, alumina, and zirconia. For example, certain embodiments oftitanium dioxide particles suitable for use in coatings of the presentinvention have a coating of silica and a coating of alumina.

Suitable species of pigment particles include zinc oxide, antimonyoxide, zirconium oxide, chromium oxide, iron oxide, lead oxide, zincsulfide, lithopone, and forms of titanium dioxide such as anatase andrutile. Preferably, the pigment particles are selected from titaniumdioxide and lead oxide. More preferably, the pigment particles areselected from rutile titanium dioxide and anatase titanium dioxide. Mostpreferably, the pigment particles are rutile titanium dioxide. A coatingcontaining two different forms of a material, such as rutile and anatasetitanium dioxide, is considered to have two different pigments.

In a coating containing two or more pigments, one pigment may have ascattering coefficient with a linear or quasi-linear relationship to thepigment volume concentration of that pigment, while the remainingpigment(s) have scattering coefficient(s) with relationship(s) that areneither linear nor quasi-linear with respect to their respective pigmentvolume concentration(s). Alternately, a coating may have a first pigmentand a second pigment, each pigment having a linear or quasi-linearrelationship to its respective pigment volume concentration.

The polymer matrix of the coating of the present invention is acontinuous medium containing the pigment particles. The polymer matrixis alternatively a homopolymer, a copolymer, an interpenetrating networkpolymer, and a blend of two or more polymers or copolymers. Suitablepolymer matrices include acrylic (co)polymers, vinyl acetate polymers,vinyl/acrylic copolymers, styrene/acrylic copolymers, polyurethanes,polyureas, polyepoxides, polyvinyl chlorides, ethylene/vinyl acetatepolymers, styrene/butadiene polymers, polyester polymers, polyethers,and the like, and mixtures thereof. Generally, the polymer matrixprovides the coating with properties such as adhesion to a substrate,gloss, abrasion resistance, and barrier properties such as moistureresistance and/or solvent resistance.

The polymer matrix is formed from a binder. The binder is a polymer or apre-polymeric material. The polymer is alternatively provided in aliquid medium such as a solution polymer, an emulsion polymer, or asuspension polymer, or is provided as a solid, such as a polymer powderor an extrusion polymer. The binder may contain reactive groups, whichupon formation of a film, crosslink to provide a crosslinked coating.

Alternatively, the polymer matrix is formed from a binder containing apolymer having reactive groups and a crosslinking agent which reactswith the reactive groups of the polymer. Conventional crosslinkingagents such as, for example, polyaziridine, polyisocyanate,polycarbodiimide, polyepoxide, polyaminoplast, polyalkoxysilane,polyoxazoline, polyamine, and a polyvalent metal compound are used,providing that the crosslinking agent does not inhibit film formation.Typically, from 0 to about 25 weight % of the crosslinking agent isused, based on the dry weight of the polymer. In one embodiment, thepolymer matrix is formed from a thermoplastic polymer and from 0 toabout 1 weight % crosslinking agent, based on dry weight of thethermoplastic polymer. In a second embodiment, the polymer matrix isformed from a polymer having reactive groups and crosslinking agent inthe range of from about 0.05 to about 25 weight %, more preferably inthe range of from about 0.1 to about 20 weight %, and most preferably inthe range of from about 1 to about 10 weight %, based on the dry weightof the polymer.

Polymers suitable as the binder are film forming at or below theapplication condition of the coating composition used to prepare thecoating of this invention. The polymers should have glass transitiontemperatures in the range of from about −60° C. to about 80° C., ascalculated by the Fox equation. The coating composition optionallycontains coalescents or plasticizers to provide the polymers witheffective film formation temperatures at or below the applicationtemperature. The level of optional coalescent is in the range of fromabout 1 weight % to about 40 weight %, based on the weight of thepolymer solids.

Alternatively, the binder is at least one pre-polymeric material whichis cured to form the polymer matrix. A pre-polymeric material is amaterial which is cured to form a polymer. A coating according to thepresent invention that is made with a pre-polymeric binder is preparedby applying a coating composition, which contains pigment particles andat least one pre-polymeric material as the binder, onto a substrate andthen polymerizing or crosslinking the at least one pre-polymericmaterial to form the polymer matrix. Examples of pre-polymeric materialsare ethylenically unsaturated monomers and oligomers, and two-partcrosslinking systems such as compositions containing isocyanate groupsand alcohol groups.

The coating of this invention optionally contains extender particles.The extender particles have an index of refraction which is similar tothe index of refraction of the polymer matrix, and do not significantlyscatter light. Extender particles have an index of refraction of lessthan 1.8 and typically greater than or equal to 1.3. Extender particlesare categorized as small extender particles, which have an averageparticle diameter of less than or equal to twice the average particlediameter of the pigment particles, and as large extender particles,which have an average particle diameter of greater than twice theaverage particle diameter of the pigment particles. In coatingscontaining more than one type of pigment particle having differentaverage particle diameters, extender particles may be a small extenderfor one type of pigment particles and a large extender for a second typeof pigment particles. Suitable extender particles include calciumcarbonate, calcium sulfate, barium sulfate, mica, clay, calcined clay,feldspar, nepheline, syenite, wollastonite, diatomaceous earth, aluminasilicates, non-film forming polymer particles, aluminum oxide, silica,and talc. Other examples of extenders include solid bead extenders, alsoknown in the art as solid bead pigments, such as polystyrene andpolyvinyl chloride beads.

The coating of this invention optionally contains secondary pigmentparticles. The secondary pigment particles have an index of refractionless than the index of refraction of the polymer matrix. Secondarypigment particles include pigment particles containing air voids, suchas polymer particles containing air voids. The air void is characterizedas having an index of refraction close to or equal to 1. The air voidvolume is considered part of the total pigment volume of the coating,while the polymer component is considered to be part of the volume ofthe extender particles. The index of refraction of the polymer componentof the secondary pigment particles is similar to or equal to the indexof refraction of the polymer matrix. Secondary pigment particlesincluding microsphere pigments such as polymer particles containing oneor more voids and vesiculated polymer particles are disclosed in U.S.Pat. No. 4,427,835; U.S. Pat. No. 4,920,160; U.S. Pat. No. 4,594,363;U.S. Pat. No. 4,469,825; U.S. Pat. No. 4,468,498; U.S. Pat. No.4,880,842; U.S. Pat. No. 4,985,064; U.S. Pat. No. 5,157,084; U.S. Pat.No. 5,041,464; U.S. Pat. No. 5,036,109; U.S. Pat. No. 5,409,776; andU.S. Pat. No. 5,510,422.

The pigment particles, the extender particles, and the secondary pigmentparticles are defined herein according to their average particlediameters and indices of refraction as follows: Index of RefractionAverage Particle Diameter Pigment particle 1.8 or greater 1 micron orsmaller small extender 1.3 to less than 1.8 twice the average diameterof particle pigment particle or smaller large extender 1.3 to less than1.8 greater than twice the average particle diameter of pigment articlesecondary pigment less than 1.3 1 micron or less particle

The coating of this invention contains from about 5 to about 40 volume %pigment particles, preferably from about 6 to about 30 volume %, andmore preferably from about 8 to about 25 volume %, based on the totalvolume of the coating. The coating contains from about 30 to about 95volume % polymer matrix, preferably from about 35 to about 90 volume %,and more preferably from about 40 to about 85 volume %, based on thetotal volume of the coating. The coating contains from 0 to about 70volume % extender particles, preferably from 0 to about 65 volume %, andmore preferably from 0 to about 60 volume %, based on the total volumeof the coating. The coating contains from 0 to about 20 volume %secondary pigment particles, preferably from 0 to about 17 volume %, andmore preferably from 0 to about 15 volume %, based on the total volumeof the coating.

The pigment volume concentration (PVC) of each type of pigment particlesis the percentage of the volume occupied by the particles of thatpigment, based on the total volume of the coating. For a coatingcontaining one or more types of pigment particles, the PVC for a singletype of pigment particles, V_(i), is expressed by equation 1a:V _(i)=100V _(p,i) /V _(c)  1awhere V_(p,i) is the volume of that single type of pigment particles andV_(c) is the total volume of the coating. The total volume of thecoating is the sum of the volumes of all components of the coatingincluding all the pigment particles, the secondary pigment particles,the polymer matrix, the small extender particles, and the large extenderparticles. The PVC is commonly reported without units or as apercentage. For example, a coating having a pigment occupying 20 volume% of the total volume of the coating has a PVC reported as 20 or 20%.

The effective PVC for a single type of pigment particles is thepercentage of the volume occupied by that type of pigment particles,based on the volume of the coating without including the large extenderparticles. The effective pigment volume concentration for a single typeof pigment particles, V_(eff,i), is expressed by equation 1b:V _(eff,i)=100 V_(p,i)/(V _(c) −V _(le))  1bwhere V_(le) is the volume of the large extender particles.

Hiding efficiency provided by a pigment in a coating is calculated fromlight scattering theory using the model described by Stieg in theOfficial Digest, 31(408), 52 (1959). This model calculates theKubelka-Munk light scattering coefficient for that pigment, S_(i), as afunction of the PVC of the particles of that pigment, according to theequation 2:S _(i) =A _(i) V _(i)(1−B _(i) V _(eff) ^(1/3))  2where A_(i) and B_(i) are constants. A coating having a pigment thatprovides theoretical hiding efficiency for the particles of thatpigment, has a light scattering coefficient, S_(i), which is linearlyproportional to V_(i). In equation 2, pigment providing theoreticalhiding efficiency has a B_(i) value equal to zero. Pigment having alight scattering coefficient with a quasi-linear relationship to thepigment volume concentration has a B_(i) value in the range of greaterthan 0 to 0.15, preferably in the range of greater than 0 to 0.14, andmore preferably in the range of greater than 0 to 0.12. The scatteringcoefficient is commonly expressed in units of reciprocal length, such asmil⁻¹ (1 mil=25.4 microns).

The value of B_(i) for a select type of pigment particles in a coatingmay be determined by measuring the Y-reflectance values of at leastthree coatings having constant composition except that the PVCs of theselect pigment particles are different. A light scattering coefficientfor each coating is calculated from the Y-reflectance value for thatcoating, Y_(j), using equation 3:S _(j) =C Y _(j)/(1−Y _(j))²  3where C is a constant. See, for example, F. W. Billmeyer and R. L.Abrams, Journal of Paint Technology, 45(579), page 6-23 (1973). Next,the value of B_(i) for the select pigment particles is determined fromthe light scattering coefficients for the coatings, using equation 4:S _(j) =A _(i) V _(i)(1−B _(i) V _(eff,i) ^(1/3))+K  4The parameter K is a constant and includes the contribution to lightscattering in the coating from sources other than the select pigmentparticles, such as other types of pigment particles, secondary pigmentparticles, and extender particles.

For example, Y-reflectance values are measured for a series of coatingscontaining titanium dioxide particles as the pigment particles, at PVCsof 10, 15, and 20. The coatings also contain an acrylic copolymer as thepolymer matrix, and calcium carbonate as large extender particles at avolume concentration of 15. In this series of coatings, the volume ofthe large extender particles remains constant at 15, while the volume ofthe polymeric matrix is 75, 70, and 65 for the coatings having PVCs of10, 15, and 20, respectively. The light scattering coefficients for thecoatings are calculated from the Y-reflectance values according toequation 3. Next, values for A_(i), B_(i), and K are calculated from thelight scattering coefficients according to equation 4.

Coatings Containing Composite Particles

The coating of this invention contains pigment particles, which areoptionally in the form of composite particles. The composite particleseach contain a single center pigment particle surrounded by a pluralityof polymer particles. The polymer particles are attached to the surfaceof each pigment particle and minimize contact between adjacent pigmentparticles. Suitable composite particles include pigment particles havingeither complete or partial surface coverage of the pigment particle bythe polymer particles, provided that the polymer particles sufficientlyencapsulate the pigment particles to prevent contact between neighboringpigment particles.

The polymer particles contained in the composite particle typically havea weight average molecular weight, Mw, of at least about 50,000,preferably of at least about 250,000, and most preferably of at leastabout 500,000, as measured by gel permeation chromatography. The polymerparticles may have an average particle diameter in the range of fromabout 10 nm to about 1 micron, preferably in the range of from about 75nm to about 500 nm, and more preferably in the range of from about 80 nmto about 200 nm. However, for composite particles containing titaniumdioxide as the pigment particle or other pigment particles of similarsize, maximum hiding power is typically obtained with polymer particleshaving average diameters in the range of from about 40 nm to about 250nm, preferably in the range of from about 50 nm to about 200 nm, andmore preferably in the range of from about 80 nm to about 150 nm. Thediameter of the polymer particles is measured by a quasi-elastic lightscattering technique.

The glass transition temperature of the polymer particles is typicallyin the range of from about −60° C. to about 120° C. Preferably thepolymer particles have glass transition temperatures of at least 20° C.,more preferably at least 35° C., and most preferably at least 50° C.

The polymer particles are typically prepared by the additionpolymerization of ethylenically unsaturated monomers. The polymerparticles are provided with functional groups by polymerizingethylenically unsaturated monomer that has a functional group or aprecursor to a functional group, referred to herein as “first monomer”.The first monomer is polymerized to prepare a homopolymer havingfunctional groups, or alternatively, is polymerized in a mixture with atleast one other ethylenically unsaturated monomer, referred to herein as“second monomer”, to prepare a copolymer having functional groups.Alternatively, the polymer particles are prepared by polymerizing afirst monomer having a group which is a precursor to a functional group.After polymerization of the polymer particle, the precursor group isconverted to provide a functional group. Examples of precursor groupsare alcohol groups, which are oxidized to either aldehyde groups orcarboxylic acid groups, or carboxylic acid groups, which are reactedwith aziridines to form amine groups.

Suitable first monomers include monomers having isocyanate groups,acetoacetoxy groups, aldehyde groups, epoxide groups, and strong acidgroups, such as phosphorus acid groups, or salts of strong acid groups.Suitable second monomers include styrene, butadiene, α-methyl styrene,vinyl toluene, vinyl naphthalene, ethylene, propylene, vinyl acetate,vinyl versatate, vinyl chloride, vinylidene chloride, acrylonitrile,methacrylonitrile, (meth)acrylamide, various C₁-C₄₀ alkyl esters of(meth)acrylic acid; for example, methyl (meth)acrylate, ethyl(meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate,cyclohexyl (meth)acrylate, n-octyl (meth)acrylate, n-decyl(meth)acrylate, n-dodecyl (meth)acrylate, tetradecyl (meth)acrylate,lauryl (meth)acrylate, oleyl (meth)acrylate, palmityl (meth)acrylate,and stearyl (meth)acrylate; other (meth)acrylates such as isobornyl(meth)acrylate, benzyl (meth)acrylate, phenyl (meth)acrylate,2-bromoethyl (meth)acrylate, 2-phenylethyl (meth)acrylate, and1-naphthyl (meth)acrylate, alkoxyalkyl (meth)acrylate, such asethoxyethyl (meth)acrylate, mono-, di-, trialkyl esters of ethylenicallyunsaturated di- and tricarboxylic acids and anhydrides, such as ethylmaleate, dimethyl fumarate, trimethyl aconitate, and ethyl methylitaconate; and carboxylic acid containing monomers, such as(meth)acrylic acid, itaconic acid, fumaric acid, and maleic acid.

The ethylenically unsaturated monomer alternatively also includes atleast one multi-ethylenically unsaturated monomer effective to raise themolecular weight and crosslink the polymer particle. Examples ofmulti-ethylenically unsaturated monomers include allyl (meth)acrylate,tripropylene glycol di(meth)acrylate, diethylene glycoldi(meth)acrylate, ethylene glycol di(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, polyalkyleneglycol di(meth)acrylate, diallyl phthalate, trimethylolpropanetri(meth)acrylate, divinylbenzene, divinyltoluene, trivinylbenzene, anddivinyl naphthalene.

Suitable polymer particles containing functional groups include bothpolymer particles having a single polymer phase and more than onepolymer phase. Polymer particles containing two or more phases havevarious morphologies including, for example, core/shell particles, coresheath particles, core/shell particles with shell phases incompletelyencapsulating the core, core/shell particles with a multiplicity ofcores, interpenetrating network particles, particles having a dipolemorphology in which each phase forms separate but connected lobes, andparticles having multiple domains on the surface of another polymerphase. Alternatively, the polymer particle has a non-spherical shapesuch as an ellipsoid or a rod-like shape. Preferably, the polymerparticle is spherical. Polymer particles containing two or more phasesmay contain the functional groups in one or more phases provided thefunctional groups are in contact with the exterior of the polymerparticle.

The polymer particles are prepared by any process which providescopolymerization of ethylenically unsaturated monomers. Suitableprocesses include suspension or emulsion polymerization, including forexample, the processes disclosed in U.S. Pat. No. 5,356,968 and U.S.Pat. No. 5,264,530. The polymer particles are also prepared by solutionpolymerization followed by the conversion of the solution polymer topolymer particles by various methods known in the art. Thepolymerization process is typically conducted in the presence of wateror an organic solvent. Emulsion polymerization techniques for preparingan aqueous dispersion of the polymer particles are well known in thepolymer arts, and include multiple stage polymerization processes.Various synthesis adjuvants such as initiators, chain transfer agents,and surfactants are optionally utilized in the polymerization.Preferably, the polymer particles are prepared by aqueous emulsionpolymerization.

Second and Third Aspects of the Invention

According to the second and third aspects of the invention, thecomposite particles have polymer particles that are covalently bondedeither directly or indirectly to the surface of the pigment particle.Such a composite particle, referred to herein as a “covalently bondedcomposite particle”, has polymer particles that are directly attached tothe pigment particle by a covalent bond between the pigment particle andthe polymer particle. Alternatively, the polymer particles areindirectly attached to the pigment particle through a linkage which hasa covalent bond with the surface of the pigment particle and a secondcovalent bond with the polymer particle.

In the second aspect of the invention, the covalent bond with thesurface of the pigment particle is formed by reacting polymer particlescontaining functional groups, referred to herein as “complementaryfunctional groups”, that are reactive with the surface of the pigmentparticle. In this aspect, the reacted complementary functional groupforms a covalent bond with the surface of the pigment particle.Alternatively, in the third aspect, the covalently bonded compositeparticle is formed containing linkages between the pigment particle andthe polymer particles. The linkage is from a select coupling agenthaving a first functional group that reacts to form a covalent bond withthe surface of the pigment particle and a second functional group thatreacts with the complementary functional group of the polymer particleto form a second covalent bond.

The covalently bonded composite particle is prepared from a pigmentparticle having a surface containing a substance selected from the groupconsisting of: metals, metal oxides, sulfides, salts, nonmetals,nonmetal sulfides, nonmetal oxides, and combinations thereof. Thesurface of the pigment particle is the native surface of the pigmentparticle. Alternatively, the surface of the pigment particle is asurface having a surface treatment thereon, which surface treatmentprovides a suitable surface for formation of covalent bonds. Thecovalent bond is formed with an atom on or at the surface of the pigmentparticle, including any optional coating or surface treatment. In thepresence of water, the surface of the pigment particle typically hashydroxyl groups.

The polymer particles suitable for preparing covalently bonded compositeparticles have a complementary functional group that is capable ofalternatively forming a covalent bond with the pigment particle and witha second functional group of a coupling agent. Suitable complementaryfunctional groups include acetoacetoxy groups, 1,3-dicarbonyl groups,aldehydes, acids, amines, epoxides, isocyanates, thioranes,isothiocyanates, alcohols, carbodiimides, aziridines, haloalkanes, andhalophenyls. According to one embodiment, the polymer particles contain,as polymerized units, first monomers selected from isocyanate monomers,such as isocyanato ethyl methacrylate, dimethyl meta-isopropenyl benzylisocyanate; acetoacetoxy monomers, such as acetoacetoxy ethyl(meth)acrylate; aldehyde monomers, such as acrolein and methacrolein;amine monomers, such as t-butyl aminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, aminobutyl (meth)acrylate, aminoethyl(meth)acrylate; aminopropyl (meth)acrylate; and oxazolidinoethyl(meth)acrylate; epoxy monomers, such as glycidyl (meth)acrylate;carboxylic acid monomers, such as (meth)acrylic acid, itaconic acid,fumaric acid, maleic acid, β-acryloxypropionic acid, ethacrylic acid,α-chloroacrylic acid, α-vinylacrylic acid, crotonic acid,α-phenylacrylic acid, cinnamic acid, chlorocinnamic acid, andβ-styrylacrylic acid; hydroxy containing monomers, such as hydroxyalkyl(meth)acrylates including 2-hydroxyethyl (meth)acrylate and3-hydroxypropyl (meth)acrylate; halogenated monomers, such asbromopropyl (meth)acrylate; and halomethyl-styrene.

The covalently bonded composite particle is formed by admixing thepigment particle with the polymer particles and reacting or allowing toreact the complementary functional group of the polymer particles andthe pigment particle. Optionally, the reaction is carried out in thepresence of a catalyst. The reacted complementary functional group formsa covalent bond with the pigment particle. A reagent is optionallyincluded to convert the complementary functional groups to more reactivegroups. In one embodiment, the covalently bonded composite particles areformed by admixing the dry pigment particles into an aqueous dispersioncontaining the polymer particles.

In one embodiment, the covalently bonded composite particles are formedby preparing an aqueous dispersion containing the pigment particles andthen admixing the aqueous pigment particle dispersion with an aqueousdispersion containing the polymer particles.

The complementary functional group that reacts to form the covalent bondof the composite particle with polymer particles attached to the surfaceof the pigment particle is selected from an aziridine, an epoxide, and athiorane. The complementary functional group reacts with hydroxyl orsulfide groups bonded to an atom, M, on the surface of the pigmentparticle. The polymer particles are attached to the pigment particle byether or thiol ether bonds. The connecting bonds are represented by thestructural formula:—C(X₁)H—C(X₂)H—Y—M—wherein:

X₁ is —OH, —SH, or —NH and X₂ is —H; and alternatively

X₂ is —OH, —SH, or —NH and X₁ is —H;

Y is O or S; and

M is an atom in the pigment particle and is selected from: Ti, Al, Zr,Si, Zn, Cr, Sn, Fe, C, and Pb.

The group —C(X₁)H—C(X₂)H— is the reacted complementary functional groupattached to the polymer particle. Fourth and Fifth Aspects of theInvention Alternatively, the covalently bonded composite particle haspolymer particles indirectly attached to the surface of the pigmentparticle through linkages, which are reacted coupling agents, and arebonded to atoms on or at the surface of the pigment particle by bondsselected from: ether bonds, thiol ether bonds, and siloxane ether bonds.The atom on or at the surface of the pigment particle is selected fromthe group consisting: of Ti, Al, Zr, Si, Zn, Cr, Sn, Fe, C, and Pb. Thelinkages are also bonded to the polymer particles by at least one groupselected from: esters, amides, ethers, urethanes, thiol ethers, amines,and ureidos.

The covalently bonded composite particle having the polymer particlesindirectly attached to the surface of the pigment particle throughlinkages is formed by admixing the pigment particle and a couplingagent. The coupling agent has a first functional group and a secondfunctional group. The first functional group of the coupling agentreacts or is allowed to react with the pigment particle to form amodified pigment particle. The reacted first functional group of thecoupling agent first forms a covalent bond with the pigment particle,thereby forming a modified pigment particle. Next, the modified pigmentparticle is admixed with the polymer particles, and the secondfunctional group of the coupling agent, which is covalently bonded tothe pigment particle, and the complementary functional groups of thepolymer particle react or are allowed to react to form the covalentlybonded composite particle. The reaction of the second functional groupof the coupling agent and the complementary functional group of thepolymer particle similarly forms a covalent bond. In such an embodiment,the polymer particles are attached to the surface of the pigmentparticle by linkages, which are molecular chains forming covalent bondswith the surface of the pigment particle and second covalent bonds withthe polymer particles. The linkages are formed by the reacted couplingagents.

The coupling agent typically has a molecular weight of less than about10,000, preferably less than about 1,000, and most preferably less thanabout 500. The reacted coupling agent has a reacted first functionalgroup that forms a covalent bond with the pigment particle and has areacted second functional group that forms a covalent bond with thepolymer particle. Alternatively, the coupling agent contains more thanone first functional group, provided that the coupling agent is bondedto only one pigment particle. Alternatively, the coupling agent alsocontains more than one second functional group. For example, a couplingagent such as 3-aminopropyl-trimethoxysilane has three trimethoxysilanegroups as the first functional groups. This coupling agent is capable offorming one, two, or three covalent bonds with the pigment particle.Similarly, the coupling agent alternatively contains more than onesecond functional group and is capable of alternatively forming morethan one covalent bond with a single polymer particle, or formingmultiple individual covalent bonds with two or more polymer particles.Suitable levels of coupling agent to form the composite particle includelevels of from 0.1 to 50 equivalents of the second function group foreach equivalent of complementary functional group.

Suitable first functional groups for attaching the coupling agent to thepigment particle include alkoxysilanes, acyloxysilanes, and silanols.

Second functional groups suitable for reaction with the complementaryfunctional groups of the polymer particle include, for example,isocyanates and isothiocyanates, which react with a complementaryfunctional group selected from alcohols, amines, ureas, and anhydrides;aldehyde groups, which react with a complementary functional groupselected from acetoacetoxy groups and amines; acetoacetoxy groups, whichreact with a complementary functional group selected from aldehydes andamines; epoxides, thioranes, and aziridines, which react with acomplementary functional group selected from alcohols, carboxylic acids,anhydrides, amines, and mercaptans; carbodiimides, which react with acomplementary functional group selected from carboxylic acids, alcohols,amines, and mercaptans; haloalkane and halomethylphenyl groups, whichreact with a complementary functional group selected from amines andcarboxylic acids; amines and thiols, which react with a complementaryfunctional group selected from epoxides, aziridines, thioranes,acetoacetoxy groups, isocyanates, isothiocyanates, and carbodiimides;and carboxylic acids, which react with a complementary functional groupselected from epoxides, aziridines, thioranes, and carbodiimides.

Examples of suitable coupling agents include: aminosilanes, such as4-aminobutylmethyldiethoxysilane,N-(2-aminoethyl)-3-aminopropyldiethylisopropoxysilane, and3-aminopropyltrimethoxysilane; epoxysilanes, such as(3-glycidoxypropyl)methyldimethoxysilane and2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; mercaptosilanes, such as(mercaptomethyl)dimethylethoxysilane,3-mercaptopropyltriisopropoxysilane, anddi-4-mercaptobutyldimethoxysilane; (meth)acrylosilanes, such as3-methacryloxypropyldimethylethoxysilane and3-acryloxypropyltrimethoxysilane; haloalkylsilanes, such as3-chloropropyltrimethoxysilane, 4-bromobutylmethyldibutoxysilane, and5-iodohexyldiethylmethoxysilane; iso(thio)cyanatosilanes, such as3-isocyanatopropyltrimethoxysilane and3-isothiocyanatopropylmethyldimethoxysilane; alcohol-functional silanes,such as 3-hydroxybutylisopropyldimethoxysilane,bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane;(propyltrimethoxysilane)sulfide terminated poly(hydroxyethylacrylate);halophenylsilanes, such as bromophenyltrimethoxysilane and(2-(iodophenyl)ethyl)ethyldimethoxysilane; halomethylphenylsilanes, suchas bis(chloromethylphenyl)dimethoxysilane andbromomethylphenyldimethylisopropoxysilane; carbodiimidesilanes, such asbis(propyltrimethoxysilane)carbodiimide andN-ethyl-N′-(propylethoxydimethoxysilane)-carbodiimide;aldehyde-functional silanes, such as 3-(trimethoxysilyl)propanal and(propyltrimethoxysilane)sulfide terminated methylmethacrylate-acroleincopolymer; and 1,3-diketone functional silanes, such as(3,5-hexandione)triethoxysilane, 3-(trimethoxysilyl)propyl acetoacetate,and (butyltriethoxysilane)sulfide terminated methylmethacrylate-butylacrylate-acetoacetoxyethyl methacrylate copolymer.

Any one of the group of reactions including the reaction between asuitable complementary functional group and the pigment particle; thereaction between the first functional group and the pigment particle;and the reaction between the second functional group and a suitablecomplementary functional group, is optionally conducted in the presenceof a catalyst. For example, tertiary amines and tin salts are suitablecatalysts for the reaction between an isocyanate group as the secondfunctional group and an alcohol as the complementary functional group.The extent of reaction of the first functional group, the secondfunctional group, and the complementary functional group is determinedusing conventional analytical techniques such as infrared spectroscopy,nuclear magnetic resonance spectroscopy, and ultraviolet-visiblespectroscopy.

Composite Particles Containing Adsorbed Polymer Particles

Composite particles containing adsorbed polymer particles are useful forpreparing coatings having theoretical or quasi-theoretical hiding. Thepolymer particles, which bear phosphorus acid groups or salts ofphosphorus acid groups as functional groups, are adsorbed onto thesurfaces of the pigment particles. The phosphorus acid groups arependant to the polymer backbone and are referred to herein as “firstphosphorus acid groups”. The composite particles containing the polymerparticles having first phosphorus acid groups are prepared from selectprocesses and from select compositions.

The polymer particles having first phosphorus acid groups are additionpolymers prepared by the polymerization of ethylenically unsaturatedmonomers including at least one phosphorus acid monomer and optionally,at least one second monomer.

The phosphorus acid monomer contains at least one ethylenic unsaturationand a phosphorus acid group. The phosphorus acid monomer isalternatively in the acid form or as a salt of the phosphorus acidgroup. Examples of phosphorus acid monomers include:

wherein R is an organic group containing an acryloxy, methacryloxy, or avinyl group; and R′ and R″ are independently selected from H and asecond organic group. The second organic group is alternativelysaturated or unsaturated.

Suitable phosphorus acid monomers include dihydrogenphosphate-functional monomers such as dihydrogen phosphate esters of analcohol in which the alcohol also contains a polymerizable vinyl orolefinic group, such as allyl phosphate, mono- or diphosphate ofbis(hydroxy-methyl) fumarate or itaconate, derivatives of (meth)acrylicacid esters, such as, for example phosphates ofhydroxyalkyl(meth)acrylates including 2-hydroxyethyl (meth)acrylate,3-hydroxypropyl (meth)acrylates, and the like. Other suitable phosphorusacid monomers are phosphonate functional monomers, such as are disclosedin WO 99/25780 A1, and include vinyl phosphonic acid, allyl phosphonicacid, 2-acrylamido-2-methylpropanephosphonic acid, α-phosphonostyrene,2-methylacrylamido-2-methylpropanephosphonic acid. Further suitablephosphorus acid monomers are 1,2-ethylenically unsaturated(hydroxy)phosphinylalkyl (meth)acrylate monomers, such as are disclosedin U.S. Pat. No. 4,733,005, and include (hydroxy)phosphinylmethylmethacrylate.

Preferred phosphorus acid monomers are dihydrogen phosphate monomers,which include 2-phosphoethyl (meth)acrylate, 2-phosphopropyl(meth)acrylate, 3-phosphopropyl (meth)acrylate, and3-phospho-2-hydroxypropyl (meth)acrylate.

In one alternative embodiment, the phosphorus acid monomer is treatedprior to polymerization to remove impurities such as saturated compoundscontaining phosphorus acid groups and salts thereof. Examples ofsaturated compounds containing phosphorus acid groups include inorganicphosphates, phosphoric acid, phosphorous acid, and 2-hydroxy ethyl esterof phosphoric acid, and their salts.

The second monomer is an ethylenically unsaturated monomer that is not aphosphorus acid monomer. Suitable second monomers include styrene,butadiene, α-methyl styrene, vinyl toluene, vinyl naphthalene, ethylene,propylene, vinyl acetate, vinyl versatate, vinyl chloride, vinylidenechloride, acrylonitrile, methacrylonitrile, (meth)acrylamide, variousC₁-C₄₀ alkyl esters of (meth)acrylic acid; for example, methyl(meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate,2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-octyl(meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate,tetradecyl (meth)acrylate, lauryl (meth)acrylate, oleyl (meth)acrylate,palmityl (meth)acrylate, and stearyl (meth)acrylate; other(meth)acrylates such as isobornyl (meth)acrylate, benzyl (meth)acrylate,phenyl (meth)acrylate, 2-bromoethyl (meth)acrylate, 2-phenylethyl(meth)acrylate, and 1-naphthyl (meth)acrylate, alkoxyalkyl(meth)acrylate, such as ethoxyethyl (meth)acrylate, mono-, di-, trialkylesters of ethylenically unsaturated di- and tricarboxylic acids andanhydrides, such as ethyl maleate, dimethyl fumarate, and ethyl methylitaconate; and carboxylic acid containing monomers such as (meth)acrylicacid, itaconic acid, fumaric acid, and maleic acid. Alternatively, thesecond monomer includes at least one multi-ethylenically unsaturatedmonomer effective to raise the molecular weight and crosslink thepolymer particle. Examples of multi-ethylenically unsaturated monomersthat are utilizable include allyl (meth)acrylate, tripropylene glycoldi(meth)acrylate, diethylene glycol di(meth)acrylate, ethylene glycoldi(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,3-butylene glycoldi(meth)acrylate, polyalkylene glycol di(meth)acrylate, diallylphthalate, trimethylolpropane tri(meth)acrylate, divinylbenzene,divinyltoluene, trivinylbenzene, and divinyl naphthalene.

The amounts and types of phosphorus acid monomer and second monomer aretypically chosen to provide a coating composition with desiredproperties for the intended application.

The polymer particles having first phosphorus acid groups useful forpreparing composite particles, which, in turn, are suitable for use inthe coating of this invention, contain, as polymerized units, phosphorusacid monomer at levels in the range of from about 0.1 to about 10 weight%, preferably from about 0.5 to about 5 weight %, and more preferablyfrom about 1 to about 3 weight %, based on the weight of the polymerparticles having first phosphorus groups. The polymer particles containat least one second monomer, as polymerized units, at levels in therange of from 90 to 99.9 weight %, preferably from 95 to 99.5 weight %,and more preferably, from 97 to 99 weight %, based on the weight of thepolymer particles.

Sixth Aspect of the Invention

The polymer particles having first phosphorus acid groups are providedas an aqueous dispersion containing the polymer particles having firstphosphorus acid groups dispersed in an aqueous medium. The aqueousmedium is characterized as being substantially free of water solublepolymer having phosphorus acid groups. The water soluble polymer havingphosphorus acid groups is an addition polymer containing at least twophosphorus acid groups that are alternatively independently locatedpendant to the backbone of the water soluble polymer and in a terminalposition. As used herein, the phosphorus acid groups of the watersoluble polymer having phosphorus acid groups are referred to as “secondphosphorus acid groups”. Contemplated are compositions in which thefirst phosphorus acid groups and the second phosphorus acid groups arethe same, and compositions in which the first phosphorus acid groups andthe second phosphorus acid groups are different. At a pH of 3 and above,the water soluble polymer having phosphorus acid groups is a componentof the aqueous medium. The water soluble polymer having phosphorus acidgroups is alternatively a homopolymer or a copolymer having a degree ofpolymerization of at least 2. The weight average molecular weight of thewater soluble polymer having phosphorus acid groups is preferably atleast 10,000, more preferably at least 25,000, and more preferably atleast 40,000, as measured by aqueous gel permeation chromatography usinga polyacrylic acid standard. In the aqueous polymer dispersioncontaining the polymer particles having first phosphorus acid groups,the term “substantially free of water soluble polymer” refers to levelsof water soluble polymer having second phosphorus acid groups in theaqueous medium defined by ratios of equivalents of second phosphorusacid groups to equivalents of first phosphorus acid group in the rangeof less than or equal to 1.5, preferably less than or equal to 1, andmore preferably, less than or equal to 0.75. In one embodiment, thelower limit for the level of water soluble polymer having secondphosphorus acid groups in the aqueous medium is zero equivalents ofsecond phosphorus acid groups.

Although not wishing to be limited to a particular theory, the inventorsbelieve that the aqueous polymerization of phosphorus acid monomer toprepare an aqueous dispersion containing polymer particles havingphosphorus acid groups also results in the formation of water solublepolymer having phosphorus acid groups. In the preparation offormulations containing composite particles from an aqueous dispersionof polymer particles having phosphorus acid groups, the water solublepolymer having phosphorus acid groups has an adverse effect on thehiding properties of coatings containing these composite particles. Thewater soluble polymer having phosphorus acid groups is believed to causebridging flocculation of the pigment particles, which leads to areduction in the hiding efficiency of the pigment particles in the driedcoating. Reduction or elimination of the water soluble polymer havingphosphorus acid groups allows the preparation of coatings with improvedhiding.

The aqueous medium of the polymer dispersion containing polymerparticles having first phosphorus acid groups optionally containsco-solvents including water miscible co-solvents such as methanol,ethanol, propanol, acetone ethylene glycol ethyl ethers, propyleneglycol propyl ethers and diacetone alcohol; and water immisciblesolvents such as propyl acetate, butyl acetate, methyl isoamyl ketone,amyl acetate, diisobutyl ketone, xylene, toluene, butanol, and mineralspirits. In one embodiment, the aqueous polymer dispersion has 0 weight% co-solvent in the aqueous medium and is referred to as“co-solvent-free”. Suitable pH values for the aqueous medium are in therange of from 2 to 12.

The aqueous polymer dispersion, containing polymer particles havingfirst phosphorus acid groups, is prepared by various processes includingprocesses that remove the water soluble polymer having phosphorus acidgroups from a composition containing the polymer particles having firstphosphorus groups, and processes that prepare the polymer particleshaving first phosphorus groups while minimizing the concomitantformation of the water soluble polymer having phosphorus acid groups.

Various processes are suitable for removing the water soluble polymerhaving phosphorus acid groups from the aqueous polymer dispersioncontaining the polymer particles having first phosphorus acid groups. Inone process, the polymer particles are phase separated from the aqueousmedium and then the aqueous medium, including the water soluble polymerhaving phosphorus acid groups, is removed. Optionally the polymerparticles are washed. Next, the polymer particles are re-dispersed intowater. The process is optionally repeated one or more times, as needed,to provide the aqueous polymer dispersion of the sixth aspect of theinvention. Other methods to separate the polymer particles from theaqueous medium include filtration and centrifugation. Other processes toremove the water soluble polymer having phosphorus acid groups from theaqueous medium include diafiltration, and contacting the aqueous mediumwith ion exchange resins and then removing the ion exchange resins.

Tenth and Eleventh Aspects of the Invention

The tenth aspect of the invention is directed towards a process forforming the aqueous polymer dispersion containing the polymer particleshaving first phosphorus groups that minimizes the formation of the watersoluble polymer having phosphorus acid groups. In this process, theaqueous polymer dispersion containing the polymer particles having firstphosphorus acid groups, according to the eleventh aspect of theinvention, is prepared by an aqueous polymerization process at low pH.The low pH polymerization process includes the polymerization ofphosphorus acid monomer in an aqueous reaction medium having a low pH.Although not wishing to be limited to a particular theory, the inventorsbelieve that in an aqueous reaction medium at low pH, the phosphorusacid monomer is protonated and is less water soluble than at higher pH.Polymerization of the protonated phosphorus acid monomer leads toincreased incorporation of the phosphorus acid monomer into the growingpolymer particles and a reduction in the formation of the water solublepolymer having phosphorus acid groups in the aqueous reaction medium. Asused herein, a low pH is a pH of less than 2, preferably less than orequal to about 1.7, and more preferably less than or equal to about 1.5.Suitable pH ranges for the low pH polymerization of the phosphorus acidmonomer include pH values in the range of from about −1 to less thanabout 2, preferably from about −1 to less than about 1.8, and morepreferably from about −1 to about 1.5. In one embodiment, the phosphorusacid monomer is polymerized at a pH in the range of from 0 to less thanabout 1.8, preferably in the range of from 0 to about 1.7, and morepreferably in the range of from 0 to about 1.6. The pH of the aqueousreaction medium is adjusted to a low pH by the addition of strong acids,such as sulfuric acid; sulfurous acid; alkyl sulfonic acids, such asmethyl sulfonic acid and alkyl ethylene oxide sulfonic acids; arylsulfonic acids, such as benzosulfonic acid; dodecyl benzene sulfonicacid; and naphthalene sulfonic acid; sulfamic acid; hydrochloric acid;iodic acid; periodic acid; selenic acid; chromic acid; nitric acid;pyrophosphoric acid; trifluoroacetic acid; dichloroacetic acid;trichloroacetic acid; dihydroxymalic acid; dihydroxytartaric acid;maleic acid; oxalic acid; and trihydroxybenzoic acid. The strong acid isadded to the aqueous reaction medium prior to the completepolymerization of the phosphorus acid monomer, including, for example,prior to the addition of the phosphorus acid monomer, during theaddition of the phosphorus acid monomer, and both before and during theaddition of the phosphorus acid monomer. Alternatively, the strong acidis added to the aqueous reaction medium after the addition of thephosphorus acid monomer, but prior to the polymerization of thephosphorus acid monomer.

The pH of the aqueous reaction medium is determined using a pH meterequipped with electrodes, such as silver chloride electrodes. The pHmeasurement is alternatively conducted on the aqueous reaction medium inthe reaction vessel or is conducted on an aliquot of the aqueousreaction medium that has been removed from the reaction vessel. The pHmeasurement is made with the tested sample of the aqueous reactionmedium at 20° C. The pH of the aqueous reaction medium is alternativelymeasured prior to, during, or after the polymerization of the phosphorusacid monomer. A pH measurement after the polymerization of thephosphorus acid monomer is made prior to the addition of substances thatchange the pH of the aqueous reaction medium.

Suitable aqueous emulsion polymerization processes for preparing theaqueous polymer dispersion containing the polymer particles having firstphosphorus acid groups include single and multiple shot batch processes.If desired, a monomer mixture containing the phosphorus acid monomer isprepared and added gradually to the reaction vessel. Optionally, themonomer composition within the reaction vessel is varied during thecourse of the polymerization, such as by altering the composition of themonomers being fed into the reaction vessel. Optionally, the monomermixture is pre-emulsified prior to addition to the aqueous reactionmedium with the optional addition of surfactant to aid in thepre-emulsification of the monomer mixture. The monomer mixtureoptionally contains one or more other materials, including water,solvents, defoamers, and strong acids. The aqueous reaction mediumoptionally includes water miscible solvents, such as methanol, ethanol,propanol, acetone, ethylene glycol ethyl ethers, propylene glycol propylethers, and diacetone alcohol; and water immiscible solvents such aspropyl acetate, butyl acetate, methyl isoamyl ketone, amyl acetate,diisobutyl ketone, xylene, toluene, butanol, and mineral spirits.Suitable polymerization processes, which include emulsion polymerizationand suspension polymerization processes, are conducted as batch,semicontinuous, or continuous processes. Single or multiple stagepolymerization techniques are suitable for the low pH process.

Temperatures suitable for the low pH aqueous emulsion polymerizationprocess are in the range of from about 20° C. to less than about 100°C., preferably in the range of from about 40° C. to about 95° C., andmore preferably in the range of from about 50° C. to about 90° C. Thereaction vessel, containing an initial quantity of water and optionallyother synthesis adjuvants, such as surfactants or acid, is typicallypreheated to a determined temperature prior to the addition of themonomer mixture. Typically, the aqueous reaction medium is agitated topromote mixing. The headspace of the reaction vessel is often flushedwith nitrogen or another inert gas to minimize the level of oxygen inthe reaction vessel.

The polymerization process for preparing the aqueous polymer dispersionhaving first phosphorus acid groups, according to the eleventh aspect ofthe invention, optionally employs a seed polymer emulsion to control thenumber of particles produced by the aqueous emulsion polymerization, asis known in the art. Suitable seed polymer emulsions include polymeremulsions having average particle diameters in the range of from about10 nm to about 60 nm. Alternatively, the seed polymer particles areprepared by adding an initial quantity of a monomer emulsion to theaqueous reaction medium and polymerizing the added monomer. A techniqueto control the particle size of the polymer particles is by adjustingthe initial surfactant charge, as is known in the art.

A polymerization initiator is typically added to the aqueous reactionmedium to initiate polymerization of the ethylenically unsaturatedmonomers. The polymerization initiator can be added at any time, priorto the addition of the phosphorus acid monomer, after the addition ofthe phosphorus acid monomer, and during the addition of the phosphorusacid monomer. Examples of suitable polymerization initiators includepolymerization initiators that thermally decompose at the polymerizationtemperature to generate free radicals. Examples include bothwater-soluble and water-insoluble species. Examples of suitable freeradical-generating initiators include persulfates, such as ammonium andalkali metal (potassium, sodium, and lithium) persulfate; azo compounds,such as 2,2′-azobis(isobutyronitrile),2,2′-azobis(2,4-dimethylvaleronitrile), and t-butyl azocyanocyclohexane;hydroperoxides, such as t-butyl hydroperoxide and cumene hydroperoxide;peroxides, such as benzoyl peroxide, caprylyl peroxide, di-t-butylperoxide, ethyl 3,3′-di-(t-butylperoxy) butyrate, ethyl3,3′-di(t-amulperoxy) butyrate, t-amylperoxy-2-ethyl hexanoate, andt-butylperoxy pivilate; peresters, such as t-butyl peracetate, t-butylperphthalate, and t-butyl perbenzoate; as well as percarbonates, such asdi(1-cyano-1-methylethyl)peroxy dicarbonate; and perphosphates.

Polymerization initiators are used alone, and alternatively, as theoxidizing component of a redox system, which also includes a reducingcomponent, such as an acid selected from the group consisting of:ascorbic acid, malic acid, glycolic acid, oxalic acid, lactic acid, andthioglycolic acid; an alkali metal sulfite, more specifically ahydrosulfite, such as sodium hydrosulfite; a hyposulfite, such aspotassium hyposulfite; and a metabisulfite, such as potassiummetabisulfite; and sodium formaldehyde sulfoxylate.

Suitable levels of initiator and the optional reducing component includeproportions of from about 0.001% to about 5% each, based on the weightof the monomers in the monomer mixture to be polymerized. Acceleratorssuch as chloride and sulfate salts of cobalt, iron, nickel, and copperare generally used in small amounts. Examples of redox catalyst systemsinclude t-butyl hydroperoxide/sodium formaldehyde sulfoxylate/Fe(II),and ammonium persulfate/sodium bisulfite/sodium hydrosulfite/Fe(II).

Chain transfer agents are optionally added to the aqueous reactionmedium to control molecular weight of the polymer particle. Examples ofchain transfer agents include mercaptans, polymercaptans, andpolyhalogen compounds. Examples of suitable chain transfer agentsinclude alkyl mercaptans, such as ethyl mercaptan, n-propyl mercaptan,n-butyl mercaptan, isobutyl mercaptan, t-amyl mercaptan, n-hexylmercaptan, cyclohexyl mercaptan, n-octyl mercaptan, n-decyl mercaptan,n-dodecyl mercaptan; 3-mercaptoproprionic acid; 2-hydroxyethylmercaptan; alcohols, such as isopropanol, isobutanol, lauryl alcohol,and t-octyl alcohol; and halogenated compounds, such as carbontetrachloride, tetrachloroethylene, and trichlorobromoethane. Generallyfrom 0 to about 10% by weight, based on the weight of the monomers inthe monomer mixture, is used to prepare the polymer particles. Othertechniques for controlling molecular weight, known in the art, includeselecting the ratio of the initiator to total monomer amount.

Catalyst and/or chain transfer agent are optionally dissolved ordispersed in separate or the same fluid medium, and gradually added tothe polymerization vessel. Monomer, either neat, dissolved, or dispersedin a fluid medium, is optionally added simultaneously with the catalystand/or the chain transfer agent. Amounts of initiator and/or catalystare optionally added to the aqueous reaction medium to “chase” residualmonomer after polymerization has been substantially completed, so as topolymerize the residual monomer, as is well known in the polymerizationarts.

The aqueous reaction medium typically contains surfactant to stabilizethe growing polymer particles during polymerization and to discourageaggregation of the polymer particles in the resulting aqueous polymerdispersion. One or more surfactants, including anionic and nonionicsurfactants, and mixtures thereof, is commonly used. Many examples ofsurfactants suitable for emulsion polymerization are given inMcCutcheon's Detergents and Emulsifiers (MC Publishing Co. Glen Rock,NF), published annually. Other types of stabilizing agents, such asprotective colloids, are optionally used. However, it is preferred thatthe amount and type of stabilizing surfactant or other type ofstabilizing agent employed during the polymerization reaction beselected so that residual stabilizing agent in the resulting aqueouspolymer dispersion does not significantly interfere with the propertiesof the aqueous polymer dispersion, the properties of compositionsincluding the aqueous polymer dispersion, or articles prepared from theaqueous polymer dispersion.

Suitable anionic surfactants include, for example, alkali fatty alcoholsulfates, such as sodium lauryl sulfate; arylalkyl sulfonates, such aspotassium isopropylbenzene sulfonate; alkali alkyl sulfosuccinates, suchas sodium octyl sulfosuccinate; and alkali arylalkylpolyethoxyethanolsulfates or sulfonates, such as sodium octyl phenoxypolyethoxyethylsulfate, having 1 to 5 oxyethylene units. Suitable nonionic surfactantsinclude, for example, alkyl phenoxypolyethoxy ethanols having alkylgroups of from 7 to 18 carbon atoms and from 6 to 60 oxyethylene units,such as, for example, heptyl phenoxypolyethoxyethanols; ethylene oxidederivatives of long chained carboxylic acids, such as lauric acid,myristic acid, palmitic acid, oleic acid, or mixtures of acids, such asthose found in tall oil, containing from 6 to 60 oxyethylene units;ethylene oxide condensates of long chained alcohols such as octyl,decyl, lauryl, or cetyl alcohols, containing from 6 to 60 oxyethyleneunits; ethylene oxide condensates of long chain or branched chainamines, such as dodecyl amine, hexadecyl amine, and octadecyl amine,containing from 6 to 60 oxyethylene units; and block copolymers ofethylene oxide sections combined with one or more hydrophobic propyleneoxide sections. High molecular weight polymers, such as hydroxyethylcellulose, methyl cellulose, and polyvinyl alcohol, are also usable.

The low pH polymerization process is suitable for preparing polymerparticles having first phosphorus acid groups with average diameters inthe range of from about 10 nm to about 1000 nm, preferably in the rangeof from about 20 nm to about 700 nm, and more preferably in the range offrom about 60 nm to about 500 nm. The low pH polymerization process ofthis invention is suitable for preparing polymer particles having firstphosphorus acid groups with molecular weights of at least about 10,000,preferably at least about 50,000, and more preferably at least about100,000.

Suitable solids ranges for the aqueous dispersion prepared by the low pHpolymerization process of this invention include from about 10 to about70 weight % polymer particles having first phosphorus acid groups, basedon the weight of the aqueous dispersion. After polymerization, the pH ofthe aqueous dispersion is typically adjusted to a pH in the range offrom about 3 to about 10.

Suitable applications of the aqueous polymer dispersion containingpolymer particles having first phosphorus acid groups dispersed in anaqueous medium, wherein the aqueous medium is substantially free ofwater soluble polymer having second phosphorus acid groups, includepaper coatings; architectural coatings, such as interior and exteriorhouse paints, wood coatings and metal coatings; coatings for leather;binders and coatings for textiles and nonwovens; adhesives; and trafficpaints such as those paints used to mark roads, pavements, and runways.

Seventh and Eleventh Aspects of the Invention

The seventh aspect of the present invention is related to a compositeparticle composition prepared from the aqueous polymer dispersioncontaining polymer particles having first phosphorus acid groups. Thecomposite particle composition contains composite particles dispersed inan aqueous medium. The aqueous medium is substantially free of watersoluble polymer having second phosphorus acid groups and having selectmolecular weights. In this composite particle composition, the compositeparticles are formed in an aqueous medium substantially free of watersoluble polymer having second phosphorus acid groups and a weightaverage molecular weight of at least 40,000, preferably at least 50,000,and more preferably at least 70,000.

Low pH aqueous emulsion polymerization of phosphorus acid monomer is asuitable method to prepare the aqueous polymer dispersion containingpolymer particles having first phosphorus acid groups, according to theeleventh aspect of the invention, which is useful for preparing acomposite particles composition. The low pH polymerization processminimizes the formation of water soluble polymer having secondphosphorus acid groups, and particularly, water soluble polymer havingsecond phosphorus acid groups and having a weight average molecularweight of at least 40,000, preferably at least 50,000, and morepreferably at least 70,000.

Eighth Aspect of the Invention

The composite particle composition including the composite particlescontaining the polymer particles having first phosphorus acid groups andan aqueous medium substantially free of water soluble polymer havingsecond phosphorus acid groups, is prepared by first admixing a firstaqueous medium containing a dispersion of pigment particles, the aqueouspolymer dispersion containing the polymer particles having firstphosphorus acid groups dispersed in a second aqueous medium, andoptionally dispersant, wherein the combined aqueous medium formed bymixing the first aqueous medium and the second aqueous medium issubstantially free of water soluble polymer having second phosphorusacid groups. Next, the polymer particles having first phosphorus acidgroups are allowed sufficient time to adsorb to the pigment particles toform the composite particles. The adsorption of the polymer particleshaving first phosphorus acid groups to the pigment particles is believedto be spontaneous and will continue until the occurrence of one of thefollowing: the polymer particles having first phosphorus acid groups arecompletely adsorbed to the surfaces of the pigment particles; thesurfaces of the pigment particles are completely covered with polymerparticles having first phosphorus acid groups; or an equilibrium isachieved between adsorbed polymer particles having first phosphorus acidgroups and polymer particles having first phosphorus acid groupsremaining dispersed in the aqueous medium of the composite particlecomposition. The time required for the completion of adsorptiontypically depends upon one or more of the following parameters: thepigment particle type, the surface treatment of the pigment particle,dispersant type and concentration, the concentrations of the pigmentparticles and the polymer particles having first phosphorus acid groups,and temperature. The time required for the complete adsorption of thepolymer particles to the pigment particles varies from instantaneouslyupon admixing of the first aqueous medium and the aqueous polymerdispersion to longer times, which are typically on the order of severalhours in duration, such as from 6 to 12 hours, although still longertimes of up to days or weeks may be required, depending on the abovementioned parameters. Where very long times are necessary for completeadsorption to occur, the composite particles so formed may be deemed notto be commercially viable. Pre-mixing the aqueous medium containing thepigment particles and the polymer particles having first phosphorus acidgroups typically reduces the time for the completion of adsorption. Forcomposites prepared with titanium dioxide particles as the pigmentparticles, adsorption of the polymer particles having first phosphorusacid groups typically requires about 4 to about 12 hours for completeadsorption. Low levels of other optional components are permissible inthe aqueous medium during the formation of the composite particle,provided these components do not substantially inhibit or substantiallyinterfere with the adsorption of the polymer particle having firstphosphorus acid groups to the pigment particle. Examples of othercomponents include co-solvents; wetting agents; defoamers; surfactants;biocides; other copolymers; and other pigments. Preferably the compositeparticle is formed in an aqueous medium in the absence of otherco-polymers and other pigments. Optionally, the composite particle isprepared with levels of dispersant in the range of from 0 to about 2weight %, preferably from 0 to about 1 weight %, and more preferablyfrom 0 to about 0.5 weight %, based on the weight of the pigmentparticle. Suitable dispersants include anionic polyelectrolytedispersants such as co-polymerized maleic acid, co-polymers includingco-polymerized acrylic acid, co-polymers including co-polymerizedmethacrylic acid, and the like; and carboxylic acids containingmolecules such as tartaric acid, succinic acid, and citric acid.

In a preferred embodiment, the polymer particles having first phosphorusacid groups are two-phase polymer particles having phosphorus groups ina single polymer phase. The two-phase polymer particles have one polymerphase with a glass transition temperature less than or equal to 40° C.and a second polymer phase with a glass transition temperature greaterthan 40° C. The difference between the glass transition temperatures ofthe two-polymer phases should be at least 10° C.

In the preparation of composite particles containing the polymerparticles having first phosphorus acid groups, the first aqueous medium,the second aqueous medium, and, optionally, the dispersant, are admixedby adding the first aqueous medium to the second aqueous medium, andalternatively by adding the second aqueous medium to the first aqueousmedium. The optional dispersant is added alternatively to the firstaqueous medium, the second aqueous medium, and to the mixture of thefirst aqueous medium and the second aqueous medium. Mixing is typicallyprovided to ensure that the pigment particles and the polymer particleshaving first phosphorus acid groups are distributed uniformly in thecombined aqueous medium. It is preferred that the first aqueous mediumcontaining the pigment particle dispersion or slurry is added to thesecond aqueous medium containing the polymer particles having firstphosphorus acid groups, rather than vice versa, so that situations inwhich there is a temporary “excess” of pigment particles relative to thepolymer particles having first phosphorus acid groups, and thepossibility of grit formation through bridging flocculation of thepolymer particles having first phosphorus acid groups due to an excessof pigment particles, are avoided.

Coating Compositions and Coatings Including the Fourth and Ninth Aspectsof the Invention

The select composite particles of the second, third, seventh, andtwelfth aspects of the invention are suitable for preparing the coatingof the first aspect of the invention. The coating is prepared from acoating composition containing the select composite particles and abinder. The coating composition is typically formed by first preparingthe composite particles and then admixing the composite particles withbinder. Next, the coating composition is applied onto a substrate anddried or allowed to dry, or cured or allowed to cure, to provide thecoating of this invention. In one embodiment, the binder is a secondpolymer. Alternatively, the second polymer is provided as an aqueouspolymer dispersion of second polymer particles. Preferably the aqueouspolymer dispersion containing the second polymer particles is preparedby aqueous emulsion polymerization. Suitable second polymers includestyrene butadiene polymers, styrene acrylate polymers, (meth)acrylatepolymers, polyvinyl chloride polymers, ethylene vinyl acetate polymers,and vinyl acetate polymers. The second polymer particles generally havean average particle diameter in the range of from about 20 nm to about 1micron, preferably from about 50 nm to about 600 nm, and more preferablyfrom about 80 nm to about 500 nm.

Suitable coating compositions to prepare the coating according to thefirst aspect of the invention include coating compositions containingcomposite particles selected from covalently bonded composite particlesand composite particles with adsorbed polymer particles having firstphosphorus acid groups, in which the composite particles are formed inan aqueous medium substantially free of water soluble polymer havingsecond phosphorus acid groups.

One embodiment provides coating compositions wherein the binder is thepolymer particles in the composite particle which coalesce to form thepolymer matrix.

In another embodiment, the binder is a prepolymeric material which is anethylenically unsaturated material selected from an ethylenicallyunsaturated monomer, an ethylenically unsaturated oligomer, and mixturesthereof. In this embodiment, the coating of this invention is preparedby applying the coating composition onto a substrate and then initiatingthe polymerization of the ethylenically unsaturated material by exposingthe coating composition containing the ethylenically unsaturatedmaterial to electromagnetic radiation such ultraviolet or visibleradiation, to ionizing radiation such as gamma rays or X-rays, orelectron beam irradiation, or by formulating the coating compositionwith a chemical initiator. Suitable ethylenically unsaturated materialsinclude monoethylenically unsaturated monomers such as C₁ to C₄₀ alkyl(meth)acrylates, hydroxyalkyl esters of ethylenically unsaturatedcarboxylic acids, isobornyl (meth)acrylate, styrene and substitutedstyrenes, carboxylic acid containing ethylenically unsaturated monomers,vinyl chloride, vinylidiene chloride; multi-ethylenically unsaturatedmonomers such as trimethylolpropane tri(meth)acrylate,trimethylolpropanepropoxylate tri(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, ethoxylatedbisphenol A di(meth)acrylates, pentaerythritolglycol di(meth)acrylate,pentaerythritol tri(meth)acrylate, tetraethyleneglycol di(meth)acrylate,melamine (meth)acrylate, diethyleneglycol di(meth)acrylate,neopentylglycol di(meth)acrylate, and triethyleneglycoltri(meth)acrylate; and ethylenically unsaturated oligomers such aspolyether acrylates, epoxy-acrylates, polyester acrylates andpolyurethane acrylates, (meth)acrylated acrylic oligomers fluorinated(meth)acrylated acrylic oligomers, polyamine acrylates; and C₄-C₈ alkanediol (meth)acrylates.

Acrylates are generally preferred over the corresponding methacrylate asacrylates typically cure at higher speeds. Coating compositionscontaining an ethylenically unsaturated material as the binder,typically contain a mixture of ethylenically unsaturated monomers oroligomers to provide the desired coating properties.

The coating composition containing ethylenically unsaturated material,which is cured by ultraviolet or visible radiation, preferably includesa photoinitiator in order initiate the polymerization and to acceleratethe speed of the polymerization reaction. Useful photoinitiators arewell known in the art and include free radical photoinitiators andcationic photoinitiators. Examples of free radical photoinitiatorsinclude benzophenone, 2,2-dialkyl-2-hydroxyacetophenone,2-methylamino-2-benzyl-1-(4-morpholinophenyl)-butan-1-one, and acylphosphines. Examples of cationic photoinitiators include aryldiazoniumsalts; diarylhalonium salts such as diaryliodonium, diarylbromonium, anddiarylchloronium salts with complex metal halide anions;triarylsulfonium salts; nitrobenzyl esters; sulfones; and triarylphosphates. Cure of the coating composition containing ethylenicallyunsaturated material using ionizing radiation, in particular, electronbeam radiation, does not require a photoinitiator although the coatingcomposition optionally contains a photoinitiator. Optionally, thecoating composition containing ethylenically unsaturated material iscured in the presence of a chemical initiator such as peroxides orazoisobutyronitrile. These chemical initiators generate radicals whichinitiate the polymerization of the ethylenically unsaturated material.The chemical initiators decompose to form radicals at room temperaturealthough an elevated temperature is often employed to achieve a fasterrate of cure.

In one embodiment, the prepolymeric material is a reactive polymer oroligomer having alkoxysilane and/or acyloxysilane groups. The reactivepolymer or oligomer is optionally formed from alkoxysilane monomerand/or acyloxysilane monomer with other silicon-free monomers. Theprepolymeric material containing the alkoxysilane and/or acyloxysilanegroups is crosslinked by a condensation reaction in the presence ofmoisture and, optionally, a catalyst. Examples of reactive polymerssuitable as a prepolymeric material containing alkoxysilane and/oracryloxysilane groups are disclosed in U.S. Pat. No. 4,499,150 and U.S.Pat. No. 4,707,515.

Alternatively, the prepolymeric material useful as a binder is a twopart curing system. The two part curing system includes a firstcomponent containing at least two reactive groups and a second componentcontaining at least two complementary reactive groups which are reactivewith the reactive groups of the first component. The second component isoften referred to as a “curing agent”. Suitable two part curing systemsinclude, for example, epoxy resins with a curing agent selected fromamine, carboxylic acid, anhydride, mercaptan, and hydroxyl containingcuring agents; amino resins with a curing agent selected from hydroxyl,carboxylic acid, and amide containing curing agents; and isocyanateresins with a curing agent selected from hydroxyl, and amine containingcuring agents. Suitable isocyanate resins include aliphatic and aromaticisocyanates. Blocked isocyanates are suitable as the isocyanate resin.

The coating composition containing the two part curing system optionallycontains a catalyst to accelerate the crosslinking reaction between thereactive groups and the complementary reactive groups. In anotherembodiment, the coating is prepared from a powder coating composition.Powder coating compositions are well known in the art and are discussedin Organic Coatings: Science and Technology, Vol. II, Z. W. Wicks, Jr.,F. N. Jones, and S. P. Pappas, John Wiley & Sons, Inc., 1994, Chap 31. Abinder for a powder coating composition such as a thermosetting powdercoating composition contains a first component, typically referred to asa primary resin and a second component, typically referred to as ahardener. Suitable binders include epoxy binders crosslinked with amaterial selected from dicyandiamide, modified dicyandiamide, andtrimellitic anhydride hardeners; polyester binders containing hydroxyland carboxylic acid groups, which are crosslinked with a materialselected from triglycidyl isocyanurate, tetra(2-hydroxyalkyl)bisamide,blocked aliphatic isocyanates, and tetramethoxymethylglycolurilhardeners; acrylic binders containing epoxy groups which are crosslinkedwith dicarboxylic acids; and acrylic binders containing hydroxyl groupswhich are crosslinked with blocked isocyanates.

The coating of this invention is typically prepared by applying acoating composition to a substrate by conventional methods such as, forexample, brushing, rolling, drawdown, dipping, with a knife or trowel,curtain coating, and spraying methods such as, for example, air-atomizedspray, air-assisted spray, airless spray, high volume low pressurespray, and air-assisted airless spray. The wet coating thickness of thecoating composition is typically in the range of from about 1 micron toabout 250 microns. The coating composition is applied onto a substrateas a single coat or multiple coats. Preferably a single coat of thecoating composition is applied. The coating is allowed to dry at ambientconditions, such as, for example, at from about 0° C. to about 35° C.,and in the alternative, dried at elevated temperatures such as, forexample, from about 35° C. to about 150° C.

In addition, the coating of this invention optionally includes othercomponents, including without limitation, other polymers, surfactants,other pigments, extenders, dyes, pearlescents, adhesion promoters,crosslinkers, dispersants, defoamers, leveling agents, opticalbrighteners, ultraviolet stabilizers, absorbing pigments, coalescents,rheology modifiers, preservatives, biocides, and antioxidants.

The coating of this invention is suitable for application onto varioussubstrates including wood; masonry; cementitious substrates such asconcrete, stucco, mortar, and concrete substrates; stone; cellulosicsubstrates such as paperboard, wallpaper, wall board, and paper; glass;metal; asphalt; leather; plastics such as polyvinyl chloride; and wovenand nonwoven material such as cloth, wool, synthetic and natural fibers,and textiles. In addition to providing a coating with improved hiding ofthe underlying substrate, the coating of this invention is suitable as aprotective coating and in the alternative, as an aesthetic coating.

The coatings of the present invention are useful as architecturalcoatings, such as interior and exterior paint coatings, includingmasonry coatings, wood coatings and treatments; floor polishes;maintenance coatings such as metal coatings; paper coatings; and trafficcoatings, such as those coatings used to provide markings on roads,pavements, and runways.

In one embodiment, the coating of this invention is a semi-gloss coatinghaving 20° gloss values in the range of from about 10 to about 50, 60°gloss values in the range of from about 50 to about 80, and 85° glossvalues in the range of from about 80 to about 95. The semi-gloss coatingoptionally contains, on a volume basis, from about 9 to about 15%pigment particles, from 0 to about 5% small extender particles, and from0 to about 10% secondary pigment particles.

In another embodiment, the coating of this invention is a sheen coatinghaving 20° gloss values in the range of from about 2 to about 10, 60°gloss values in the range of from about 10 to about 30, and 85° glossvalues in the range of from about 10 to about 30. The sheen coatingoptionally contains, on a volume basis, from about 9 to about 15%pigment particles, from about 10 to about 20% large extender particles,and from 0 to about 10% secondary pigment particles.

In another embodiment, the coating of this invention is a flat coatinghaving 20° gloss values in the range of from 0 to about 5, 60° glossvalues in the range of from 0 to about 5, or 85° gloss values of from 0to about 5. The flat coating optionally contains on a volume basis, fromabout 6 to about 12% pigment particles, from about 25 to about 40% largeextender particles, and from 0 to about 15% secondary pigment particles.

EXAMPLES

The examples which follow illustrate the several aspects of thecomposition and the process of the present invention. These examples areintended to aid those skilled in the art in understanding the presentinvention. The present invention is, however, in no way limited thereby.The abbreviation “g” represents “grams”. The abbreviation “mg”represents “milligrams”.

Method to Determine Value of B for a Species of Pigment Particles in aCoating

The B value for a coating containing a particular species of pigmentparticles, which are at a pigment volume concentration (PVC) having avalue represented by “V” in the coating, where the coating is referredto as “Coating-V”, is determined by preparing a series of coatingsincluding coatings having pigment volume concentrations for the speciesof pigment particles of 0.2V, 0.4V, 0.6V, 0.8V, and V. For thosecoatings having PVC values that are fractional values of V, the PVC's ofany other species of primary pigments and secondary pigments, and thevolume concentrations of extenders and dyes are maintained at the samelevels as in Coating-V.

The coatings are prepared by combining the components of the coatingcompositions in the same order using the same method of preparation. Allcoating compositions have the same volume solids. The coatingcompositions are applied using a single type of applicator onto OpacityCharts (The Leneta Company, Form 3B) and are allowed to dry or cureunder the identical conditions for the same period of time. The OpacityCharts have white and black sections.

The Y-reflectance value for each coating, Y_(j), is measured over boththe black and white sections of the chart using a colorimeter, such as aPacific Scientific Colorguard Colorimeter (supplied by Gardner Ineotec,MD). The thickness of the coating must be large enough so that theY-values measured over the black and white section of the chart are thesame. If the Y-value for Coating-V is less than 0.75, the coatingcompositions for the series of coatings are tinted with 0.79 kg (1.75lb) of Supronil™ HK Black Liquid (Clarient AG Corp., RI) per 378.5liters (100 gallons) of the coating compositions.

The scattering coefficients for each coating, Sj, are calculated byusing the equation S=2.578Y_(j)/(1-Y_(j))², where Y is a number from0-1. The value of B for the Coating-V is calculated by fitting thevalues of S_(j) to equation 4.

Determination of the Level of Water Soluble Polymer Having PhosphorusAcid Groups

To a centrifuge tube, 29.0 g of an aqueous polymer dispersion containingpolymer particles bearing phosphorus acid groups was added. The samplewas centrifuged at 50,000 rotations per minute (rpm) at a temperature of15° C. for 2 hours. A portion of the serum phase was removed from thesample and dried at room temperature. A stock solution was preparedcontaining 0.05 g methyl phosphonic acid, 0.10 g ammonia (28%), and 4.85g deuterated water (D₂O). The serum phase solids were dissolved in 1.0 gof the stock solution. The concentration of the water soluble polymerhaving phosphorus acid groups was determined using phosphorus-31 nuclearmagnetic resonance spectroscopy (NMR) by calculating the ratio of thearea of the broad peak for the water soluble polymer containingphosphorus acid groups at 4.7 ppm to the area of the peak for methylphosphonate at 21.6 ppm.

Determination of the Level of Phosphorus Groups in the Polymer Particles

The equivalents of phosphorus acid groups in the polymer particles weredetermined from the equivalents of phosphorus acid monomer used in thepreparation of the polymer particles, minus the equivalents of watersoluble polymer having phosphorus acid groups, as determined byphosphorus-31 NMR.

Where the equivalents of phosphorus acid groups used in the preparationof the polymer particles were not known, the equivalents of phosphorusacid groups in the polymer particles were determined by first measuringthe total equivalents of phosphorus acid groups in the aqueous polymerdispersion using atomic absorption spectroscopy, and then subtractingthe equivalents of water soluble polymer having phosphorus acid groups,as determined by phosphorus-31 NMR.

Example 1 Preparation of Composite Particles with Covalently BondedPolymer Particles Example 1.1 Preparation of Composite Particles fromTitanium Dioxide Particles and Isocyanate Functional Polymer Particles

Composite particles having covalently bonded polymer particles wereprepared by the reaction of isocyanate functional polymer particles andtitanium dioxide particles functionalized with amine groups.

Preparation of Isocyanate Functional Polymer Particles

A 3-liter, four necked round bottom flask was equipped with a paddlestirrer, a thermometer, nitrogen inlet, and a reflux condenser. To theflask was added 1100 g deionized water. The deionized water was heatedto a temperature of 85° C. under a nitrogen atmosphere. A mixture of11.6 g sodium lauryl sulfate (SLS) (28% solids) in 10 g deionized waterwas added to the flask, followed by a mixture of 3.8 g sodium carbonatein 50 g deionized water. These additions were immediately followed bythe addition of a solution of 3.9 g sodium persulfate in 50 g deionizedwater. After the addition of the sodium persulfate solution, a monomeremulsion (ME), which was prepared by mixing 320 g deionized water, 10 gSLS, 492.5 g butyl acrylate, 530.3 g methyl methacrylate, 43.2 g3-isopropenyl-α,α-dimethylbenzyl isocyanate, and 14.0 g methacrylicacid, was added to the flask at a rate of 6 g/minute at a temperature of85° C. for 30 minutes. After the 30 minutes, the feed rate was increasedto 12 grams/minute. When the ME feed was complete, the reaction was heldat a temperature of 85° C. for a period of 15 minutes and then thecontents of the flask was cooled to room temperature and filtered toremove any coagulum. The dispersion containing the isocyanate functionalpolymer particles had a solids content of 38.5 weight %, an averageparticle diameter of 85 nm, and a pH of 6.0.

Preparation of Functionalized Pigment Particles

The titanium dioxide particles functionalized with amine groups wereprepared by treating titanium dioxide particles with a coupling agentcontaining alkoxysilane groups as the first functional group and anamine group as the second functional group. The alkoxysilane groups werereacted with the titanium dioxide particles to attach the coupling agentto the titanium dioxide particles with covalent bonds.

A mixture of 95 g ethanol and 5 g water was placed in a grind pot whichwas then placed on a Premier Mill dispersator (manufactured by PremierMill Corp., Reading, Pa.) equipped with a disk blade. To the grind pot,400 g TiPure™ R-706 titanium dioxide (TiPure is a trademark of E.I.DuPont de Nemours and Company, Wilmington, Del.) was added with mixing.Next, the mixture was ground at 2000 rpm for a period of 15 minutes todisperse the titanium dioxide particles. The mill speed was decreased togentle stirring, followed by the addition of 4 g of3-aminopropyl-trimethoxysilane. The mixture was stirred for 1 hour.Next, the mixture was transferred to a plastic bucket and the ethanoland water were allowed to evaporate at room temperature to providetitanium dioxide particles functionalized with amine groups as thefunctionalized pigment particles.

The functionalized titanium dioxide particles were provided as anaqueous dispersion by first adding 75.0 g of water to a grind pot. Next,300 g of the functionalized titanium dioxide particles were added to thegrind pot with mixing using a Premier Mill dispersator equipped with adisk blade and ground at 2000 rpm for 20 minutes to provide the aqueousdispersion containing functionalized titanium dioxide particles.

Preparation of Composite Particles

Composite particles according to the present invention were prepared byadding dropwise 140 g of the aqueous dispersion containing thefunctionalized titanium dioxide particles, to 180 g of the isocyanatefunctional polymer particle dispersion, with mixing. The resultingcomposite particle dispersion was placed on a roller for at least 12hours. The final composite particle dispersion had a solids level of56.7 weight %. The composite particles contained 61.5 weight % titaniumdioxide particles and 38.5 weight % polymer particles.

Example 1.2 Preparation of Composite Particles From Titanium DioxideParticles and Acetoacetoxy Functional Polymer Particles

Composite particles were prepared by the reaction of acetoacetoxyfunctional polymer particles and titanium dioxide particlesfunctionalized with aldehyde groups.

Preparation of Aldehyde Containing Coupling Agent

A coupling agent containing an alkoxysilane group as the firstfunctional group and an aldehyde group as a second functional group wasprepared by first adding 75.0 g butyl acetate to a 250 ml round bottomflask equipped with a reflux condenser, magnetic stirrer, thermocouple,and a nitrogen inlet tube. The contents of the flask was swept withnitrogen and heated to a temperature of 88° C. Next, a solution of 0.05g Vazo™ 67 initiator (Vazo is a trademark of E.I. DuPont de Nemours andCo., Wilmington, Del.) in 2.5 g butyl acetate was added to the flask. Amonomer mixture, which contained 25 g butyl acetate, 12.5 g methylmethacrylate, 12.5 g hydroxyethyl methacrylate, and 0.8 g of3-mercaptopropyltrimethoxysilane, was added dropwise to the flask in a30 minute period. The contents of the flask was allowed to stand for aperiod of 15 minutes, and then the temperature was increased to 95° C.and maintained at a temperature of 95° C. for 40 minutes. The contentsof the flask was then allowed to cool to room temperature and then 55.5g anhydrous dimethyl sulfoxide was added, followed by the addition of4.9 g diisopropylcarbodiimide and 1.1 g pyridine-hydrochloric aciddissolved in 5 g dimethylsulfoxide. The contents of the flask wasallowed to sit for 72 hours. A white precipitate formed and was removedby filtration. The remaining mixture contained an alkoxysilaneterminated co-oligomer of methylmethacrylate and 2-hydroxy acetaldehydeester of methacrylic acid as an aldehyde functional alkoxysilanecoupling agent at 9.8 weight % solids.

Preparation of Functionalized Pigment Particles

The titanium dioxide particles functionalized with aldehyde groups wereprepared by treating titanium dioxide particles with a coupling agentcontaining alkoxysilane groups and an aldehyde group. The alkoxysilanegroups were reacted with the titanium dioxide particles to attach thecoupling agent to the titanium dioxide particles with covalent bonds.

A mixture of 95 g ethanol and 5 g water was placed in a grind pot whichwas then placed on a Premier Mill dispersator equipped with a diskblade. To the grind pot, 400 g TiPure™ R-706 titanium dioxide (TiPure isa trademark of E.I. DuPont de Nemours and Company) was added withmixing. The mixture was then ground at 2000 rpm for 20 minutes todisperse the titanium dioxide particles. Next, 80 g of the aldehydefunctional alkoxysilane coupling agent was added, followed by theaddition of 3 drops of hydrochloric acid. The mixture was ground for anadditional 5 minutes. The mill speed was decreased to gentle stirringand the mixture was stirred for 25 minutes. The mixture was transferredto a plastic bucket and the ethanol and water were allowed to evaporateat room temperature to provide titanium dioxide particles functionalizedwith aldehyde groups as the functionalized pigment particles.

An aqueous dispersion containing the functionalized titanium dioxideparticles was prepared by first adding 104.6 g water, 6.1 g Tamol™ 731dispersant (Tamol is a trademark of Rohm and Haas Company, Philadelphia,Pa.), 6.9 g Colloid 643 dispersant (manufactured by Allied ColloidsLimited Company, UK), and 1.1 g sodium hydroxide (50 weight % solution)to a grind pot. The contents of the grind pot was mixed using a PremierMill dispersator equipped with a disk blade followed by the addition of384 g of the aldehyde functional titanium dioxide particles. The mixturewas ground at 2000 rpm for 20 minutes to provide the aqueous dispersioncontaining aldehyde functional titanium dioxide particles.

Preparation of Composite Particles

An aqueous dispersion containing the composite particles of thisinvention was prepared by adding dropwise and with mixing, 46.8 g of theaqueous dispersion containing the aldehyde functional titanium dioxideparticles to 51.4 g of Rhoshield™ 3188 polymer dispersion (Rhoshield isa trademark of Rohm and Haas Company). Rhoshield™ 3188 polymer is anacetoacetoxy-functional polymer particle dispersion supplied at 40weight % solids and has an average particle diameter of 120 nm. Theresulting composite particle dispersion was placed on a roller for atleast 12 hours prior to formulation into a coating composition. Theresulting composite particle dispersion had a solids level of 56.6weight %. The composite particles contained 63 weight % titanium dioxideparticles and 37 weight % polymer particles.

Example 2 Preparation of Composite Particles with Adsorbed PolymerParticles

The following abbreviations are used in this example: surfactant-Asurfactant having an average composition of lauryl- (ethylene oxide)₄sodium sulfate; 30 wt % solids SLS sodium lauryl sulfate; 28 wt % ME-1first monomer emulsion ME-2 second monomer emulsion ME-3 third monomeremulsion PEM phosphoethyl methacrylateThe ammonium hydroxide was at 28% solids.

Preparation of Phosphorus Acid Monomers Preparation of PhosphorylatedCaprolactone 2-(Methacryloyloxy)Ethyl Ester

The reactor was equipped with an agitator, a thermocouple, a reagentfeeding line, an oxygen stream, and temperature control. To the reactorwas added 47 g of polyphosphoric acid. The contents of the reactor washeated to a temperature of 65° C. with mixing. A mixture of 101 g ofcaprolactone 2-(methacryloyloxy)ethyl ester and 0.1 g of 4-methoxyphenolwas added to the reactor over a period of 3 hours while maintaining thecontents of the reactor at a temperature of 65° C. After the addition ofthe mixture, the contents of the reactor was maintained at a temperatureof 65° C. for 19 hours with vigorous stirring. Next, the contents of thereactor was cooled to room temperature and 25 g of methyl methacrylatewas added to the reactor. The resulting monomer contained 60 wt. %phosphorylated caprolactone 2-(methacryloyloxy)ethyl ester and 15 wt. %methyl methacrylate.

Preparation of Phosphorylated Hydroxybutyl Methacrylate

The reactor was equipped with an agitator, a thermocouple, a reagentfeeding line, an oxygen stream, and temperature control. To the reactorwas added 49 g of polyphosphoric acid. The contents of the reactor washeated to a temperature of 65° C. with mixing. A mixture of 68 g ofhydroxybutyl methacrylate and 66 mg of 4-methoxyphenol was added to thereactor over a period of 3 hours while maintaining the contents of thereactor at a temperature of 65° C. After the addition of the mixture,the contents of the reactor was maintained at a temperature of 65° C.for 19 hours with vigorous stirring. Next, the contents of the reactorwas cooled to room temperature and 20 g of methyl methacrylate was addedto the reactor. The resulting monomer contained 63 wt. % phosphorylatedhydroxybutyl methacrylate and 15 wt. % methyl methacrylate.

Preparation of Mono-Phosphonoethyl Methacrylate

The reactor was equipped with an agitator, a thermocouple, a reagentfeeding line, an oxygen stream, and temperature control. To the reactorwas added 98 g of pyrophosphoric acid, which was heated to a temperatureof 65° C. A mixture of 130 g hydroxyethyl methacrylate and 0.1 g of4-methoxyphenol was added to the reactor over a period of 3 hours. Afterthe addition of the mixture, the contents of the reactor was maintainedat a temperature of 65° C. for 17 hours with vigorous stirring. Thecontents of the reactor was cooled to room temperature and 16.4 g ofmethyl methacrylate was added. The resulting monomer contained 35 wt. %phosphonoethyl methacrylate and 15 wt. % methyl methacrylate.

Purification of Phosphoethyl Methacrylate

A sample of unpurified phosphoethyl methacrylate containing 20 weight %free phosphoric acid was purified by first adding 350 g of saturatedsodium chloride solution (5.3 M NaCl), 200 g unpurified phosphoethylmethacrylate, and 270 g butyl acetate to a 1 liter separatory funnel.The mixture was shaken for 1 to 2 minutes and then allowed to separateinto two phases. The lower aqueous phase was drained from the separatoryfunnel. The organic top phase was then transferred to a container. Next,10 g magnesium sulfate was added to the organic phase and the organicphase was mixed for 10 minutes. The organic phase was then filtered toremove the magnesium sulfate. The butyl acetate was removed from theorganic phase on a Buchii Rota-Evaporator to yield purified phosphoethylmethacrylate containing 1 weight % free phosphoric acid.

Preparation of Aqueous Dispersions

Aqueous dispersions containing polymer particles having first phosphorusacid groups were prepared. The reactor used to prepare these dispersionsand comparative dispersion was a 3-liter, four necked round bottom flaskequipped with a paddle stirrer, a thermometer, nitrogen inlet, and areflux condenser.

Example 2.1

To the flask was added 800 g deionized water and 0.7 g concentratedsulfuric acid. The contents of the flask was heated to a temperature of85° C. under a nitrogen atmosphere. A mixture of 5.0 g surfactant-A in 5g deionized water was added to the flask followed by the addition of amixture of 2.4 g sodium persulfate in 25 g deionized water. After theaddition of the sodium persulfate solution, ME-1, which was prepared bymixing 260 g deionized water, 20 g surfactant-A, 132 g butyl acrylate,444 g methyl methacrylate, 6.0 g acrylic acid, 18.0 g purifiedphosphoethyl methacrylate, and 5.0 g sulfuric acid, was added to theflask at a rate of 7.0 g/minute at a temperature of 85° C. When additionof the ME-1 was completed, the contents of the flask was held at atemperature of 85° C. for a period of 15 minutes to allow polymerizationof the monomers, and then cooled to room temperature. Next, 16 gammonium hydroxide was added to the flask and the contents of the flaskwas filtered to remove any coagulum. The resulting dispersion,containing the polymer particles, had a solids content of 33.0 weight %,an average particle diameter of 85 nm, and a pH of 9.0. The polymerparticles had a glass transition temperature of 50° C.

Example 2.2

To the flask was added 800 g deionized water and 0.7 g concentratedsulfuric acid. The contents of the flask was heated to a temperature of85° C. under a nitrogen atmosphere. A mixture of 3.0 g surfactant-A in10 g deionized water was added to the flask, followed by the addition ofME-1, prepared by mixing 12 g deionized water, 1.0 g surfactant-A, 7.9 gbutyl acrylate, 27.7 g methyl methacrylate, and 0.4 g methacrylic acid.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for a period of 10 minutes to allow polymerization of theadded monomers. After 10 minutes, ME-2 containing 170 g deionized water,16.0 g surfactant-A, 124.1 g butyl acrylate, 416.3 g methylmethacrylate, 5.6 g acrylic acid, 18.0 g purified phosphoethylmethacrylate, and 5.0 g sulfuric acid was added to the flask at a rateof 7.5 g/minute at a temperature of 85° C. When addition of the ME-2 wascomplete, the contents of the flask was held at a temperature of 85° C.for a period of 15 minutes and then cooled to room temperature. Next, 16g ammonium hydroxide was added to the flask and the contents of theflask was filtered to remove any coagulum. The resulting dispersion,containing the polymer particles, had a solids content of 35.0 weight %,an average particle diameter of 128 nm, and a pH of 8.6. The resultingaqueous polymer dispersion contained a ratio of second phosphorus acidgroup equivalents to first phosphorus acid group equivalents of lessthan 0.6.

Example 2.3

To the flask was added 800 g deionized water and 0.7 g concentratedsulfuric acid. The contents of the flask was heated to a temperature of85° C. under a nitrogen atmosphere. A mixture of 3.0 g surfactant-A in10 g deionized water was added to the flask, followed by the addition ofME-1, which was prepared by mixing 12 g deionized water, 1.0 gsurfactant-A, 7.9 g butyl acrylate, 27.7 g methyl methacrylate, and 0.4g methacrylic acid. Following addition of the ME-1, a mixture of 2.4 gsodium persulfate in 20 g deionized water was added to the flask and thecontents of the flask was held for a period of 10 minutes to allowpolymerization of the added monomers. After 10 minutes, ME-2, whichcontained 170 g deionized water, 16.0 g surfactant-A, 124.1 g butylacrylate, 416.3 g methyl methacrylate, 5.6 g methacrylic acid, 18.0 gpurified phosphoethyl methacrylate, and 5.0 g sulfuric acid, was addedto the flask at a rate of 7.5 g/minute at a temperature of 85° C. Whenaddition of the ME-2 was complete, the contents of the flask was held ata temperature of 85° C. for a period of 15 minutes and then cooled toroom temperature. Next, 16 g ammonium hydroxide was added to the flaskand the contents of the flask was filtered to remove any coagulum. Theresulting dispersion, containing the polymer particles, had a solidscontent of 34.8 weight %, an average particle diameter of 145 nm, and apH of 9.0.

Example 2.4

To the flask was added 800 g deionized water and 0.7 g concentratedsulfuric acid. The contents of the flask was heated to a temperature of85° C. under a nitrogen atmosphere. A mixture of 3.0 g surfactant-A in10 g deionized water was added to the flask, followed by addition ofME-1, which was prepared by mixing 12 g deionized water, 1.0 gsurfactant-A, 8.0 g butyl acrylate, and 28.0 g methyl methacrylate.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for a period of 10 minutes to allow polymerization of theadded monomers. After 10 minutes, ME-2, which contained 170 g deionizedwater, 16.0 g surfactant-A, 124.1 g butyl acrylate, 422.0 g methylmethacrylate, 18.0 g purified phosphoethyl methacrylate, and 5.0 gsulfuric acid, was added to the flask at a rate of 7.5 g/minute at atemperature of 85° C. When addition of the ME-2 was complete, thecontents of the flask was held at a temperature of 85° C. for a periodof 15 minutes and then cooled to room temperature. Next, 16 g ammoniumhydroxide was added to the flask and the contents of the flask wasfiltered to remove any coagulum. The resulting dispersion, containingthe polymer particles, had a solids content of 35.6 weight %, an averageparticle diameter of 160 nm, and a pH of 8.9.

Example 2.5

To the flask was added 800 g deionized water and 0.7 g concentratedsulfuric acid. The contents of the flask was heated to a temperature of85° C. under a nitrogen atmosphere. A mixture of 3.0 g surfactant-A in10 g deionized water was added to the flask, followed by the addition ofME-1, which was prepared by mixing 12 g deionized water, 1.0 gsurfactant-A, 8.0 g butyl acrylate, and 28.0 g methyl methacrylate.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for a period of 10 minutes to allow polymerization of theadded monomers. After 10 minutes, ME-2, which contained 170 g deionizedwater, 16.0 g surfactant-A, 124.1 g butyl acrylate, 422.0 g methylmethacrylate, 18.0 g purified phosphoethyl methacrylate, and 5.0 gsulfuric acid, was added to the flask at a rate of 7.5 g/minute at atemperature of 85° C. After addition of 75% of the ME-2, a solution of 5g ammonium hydroxide and 10 g deionized water was added to the flaskwhile continuing addition of the remaining ME-2. After complete additionof the ME-2, the contents of the flask was held at a temperature of 85°C. for a period of 15 minutes and then cooled to room temperature. Next,11 g ammonium hydroxide was added and the contents of the flask wasfiltered to remove any coagulum. The resulting dispersion, containingpolymer particles, had a solids content of 35.3 weight %, an averageparticle diameter of 110 nm, and a pH of 8.7.

Example 2.6

To the flask was added 800 g deionized water and 3.0 g concentratedsulfuric acid. The contents of the flask was heated to a temperature of85° C. under a nitrogen atmosphere. A mixture of 3.0 g surfactant-A in10 g deionized water was added to the flask, followed by addition ofME-1, which was prepared by mixing 12 g deionized water, 1.0 gsurfactant-A, 8.0 g butyl acrylate, and 28.0 g methyl methacrylate.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for a period of 10 minutes to allow polymerization of theadded monomers. After 10 minutes, ME-2, which contained 80 g deionizedwater, 8.0 g surfactant-A, 66.0 g butyl acrylate, 216.0 g methylmethacrylate, and 18.0 g purified phosphoethyl methacrylate, was addedto the flask at a rate of 7.5 g/minute at a temperature of 85° C. Aftercomplete addition of the ME-2, a solution of 4.0 g ammonium hydroxideand 10 g deionized water was added to the flask. Next, ME-3, whichcontained 80 g deionized water, 8.0 g surfactant-A, 72.0 g butylacrylate, and 228.0 g methyl methacrylate, was fed to the flask at arate of 12.5 g/minute. Upon complete addition of the addition of theME-3, the contents of the flask was held at a temperature of 85° C. fora period of 15 minutes, and then cooled to room temperature. Next, 10 gammonium hydroxide was added and the contents of the flask was filteredto remove any coagulum. The resulting dispersion, containing polymerparticles, had a solids content of 36.4 weight %, an average particlediameter of 123 nm, and a pH of 8.9.

Example 2.7

To the flask was added 800 g deionized water and 3.0 g concentratedsulfuric acid. The contents of the flask was heated to a temperature of85° C. under a nitrogen atmosphere. A mixture of 3.0 g surfactant-A in10 g deionized water was added to the flask, followed by addition ofME-1, which was prepared by mixing 12 g deionized water, 1.0 gsurfactant-A, 8.0 g butyl acrylate, and 28.0 g methyl methacrylate.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for a period of 10 minutes to allow polymerization of theadded monomers. After 10 minutes, ME-2, which contained 80 g deionizedwater, 8.0 g surfactant-A, 66.0 g butyl acrylate, 216.0 g methylmethacrylate, and 18.0 g purified phosphoethyl methacrylate, was addedto the flask at a rate of 7.5 g/minute at 85° C. After complete additionof the ME-2, ME-3, which contained 80 g deionized water, 8.0 gsurfactant-A, 72.0 g butyl acrylate, and 228.0 g methyl methacrylate,was fed to the flask at a rate of 12.5 g/minute. Upon complete additionof the addition of ME-3, the contents of the flask was held at atemperature of 85° C. for a period of 15 minutes and then cooled to roomtemperature. Next, 16 g ammonium hydroxide was added and the contents ofthe flask was filtered to remove any coagulum. The resulting dispersion,containing polymer particles, had a solids content of 36.3 weight %, anaverage particle diameter of 126 nm, and a pH of 9.2.

Example 2.8

To the flask was added 800 g deionized water and 3.0 g concentratedsulfuric acid. The contents of the flask was heated to a temperature of85° C. under a nitrogen atmosphere. A mixture of 3.0 g surfactant-A in10 g deionized water was added to the flask, followed by addition ofME-1, which was prepared by mixing 12 g deionized water, 1.0 gsurfactant-A, 8.0 g butyl acrylate, and 28.0 g methyl methacrylate.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for a period of 10 minutes to allow polymerization of theadded monomers. After 10 minutes, ME-2, which contained 80 g deionizedwater, 8.0 g surfactant-A, 96.0 g ethyl acrylate, 186.0 g methylmethacrylate, and 18.0 g purified phosphoethyl methacrylate, was addedto the flask at a rate of 7.5 g/minute at a temperature of 85° C. Aftercomplete addition of the ME-2, ME-3, which contained 80 g deionizedwater, 8.0 g surfactant-A, 72.0 g butyl acrylate, and 228.0 g methylmethacrylate, was then fed to the flask at a rate of 12.5 g/minute. Uponcomplete addition of the ME-3, the contents of the flask was held at atemperature of 85° C. for a period of 15 minutes and then cooled to roomtemperature. Next, 16 g ammonium hydroxide was added and the contents ofthe flask was filtered to remove any coagulum. The resulting dispersion,containing polymer particles, had a solids content of 36.4 weight %, anaverage particle diameter of 127 nm, and a pH of 9.4.

Example 2.9

To the flask was added 800 g deionized water and 3.0 g concentratedsulfuric acid. The contents of the flask was heated to a temperature of85° C. under a nitrogen atmosphere. A mixture of 3.0 g surfactant-A in10 g deionized water was added to the flask, followed by addition ofME-1, which was prepared by mixing 12 g deionized water, 1.0 gsurfactant-A, 8.0 g butyl acrylate, and 28.0 g methyl methacrylate.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for a period of 10 minutes to allow polymerization of theadded monomers. After 10 minutes, ME-2 containing 80 g deionized water,8.0 g surfactant-A, 66.0 g butyl acrylate, 212.8 g methyl methacrylate,and 21.2 g unpurified phosphoethyl methacrylate was added to the flaskat a rate of 7.5 g/minute at a temperature of 85° C. After completeaddition of ME-2, a solution of 4.0 g ammonium hydroxide and 10 gdeionized water was added to the flask. Next, ME-3 containing 80 gdeionized water, 8.0 g surfactant-A, 72.0 g butyl acrylate, and 228.0 gmethyl methacrylate was added to the flask at a rate of 12.5 g/minute.Upon complete addition of the ME-3, the contents of the flask was heldat a temperature of 85° C. for a period of 15 minutes and then cooled toroom temperature. Next, 12 g ammonium hydroxide was added and thecontents of the flask was filtered to remove any coagulum. The resultingdispersion containing polymer particles had a solids content of 34.4weight %, an average particle diameter of 118 nm, and a pH of 9.0.

Example 2.10

To the flask was added 800 g deionized water and 3.0 g concentratedsulfuric acid. The contents of the flask was heated to a temperature of85° C. under a nitrogen atmosphere. A mixture of 3.0 g surfactant-A in10 g deionized water was added to the flask followed by the addition ofME-1, which was prepared by mixing 12 g deionized water, 1.0 gsurfactant-A, 8.0 g butyl acrylate, and 28.0 g methyl methacrylate.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for a period of 10 minutes to allow polymerization of theadded monomers. After 10 minutes, ME-2, which contained 170 g deionizedwater, 16.0 g surfactant-A, 124.1 g butyl acrylate, 422.0 g methylmethacrylate, and 18.0 g purified phosphoethyl methacrylate, was addedto the flask at a rate of 7.5 g/minute at a temperature of 85° C. Afterthe complete addition of the ME-2, the contents of the flask wasmaintained at a temperature of 85° C. and then cooled to roomtemperature. Next, 16 g ammonium hydroxide was added and the contents ofthe flask was filtered to remove any coagulum. The resulting dispersioncontaining the polymer particles had a solids content of 36.0 weight %,an average particle diameter of 120 nm, and a pH of 9.5.

Example 2.11

To the flask was added 800 g deionized water and 3.0 g concentratedsulfuric acid. The contents of the flask was heated to a temperature of85° C. under a nitrogen atmosphere. A mixture of 3.0 g surfactant-A in10 g deionized water was added to the flask followed by the addition ofME-1, which was prepared by mixing 12 g deionized water, 1.0 gsurfactant-A, 8.0 g butyl acrylate, and 28.0 g methyl methacrylate.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for a period of 10 minutes to allow polymerization of theadded monomers. After 10 minutes, ME-2, which contained 110 g deionizedwater, 10.5 g surfactant-A, 88.0 g butyl acrylate, 294.0 g methylmethacrylate, and 18.0 g purified phosphoethyl methacrylate, was addedto the flask at a rate of 7.5 g/minute at a temperature of 85° C. Aftercomplete addition of the ME-2, a solution of 4.0 g ammonium hydroxideand 10 g deionized water was added to the flask. Next, ME-3, whichcontained 50 g deionized water, 5.5 g surfactant-A, 48.0 g butylacrylate, and 152.0 g methyl methacrylate, was added to the flask at arate of 12.5 g/minute. Upon complete addition of the ME-3, the contentsof the flask was maintained at a temperature of 85° C. for a period of15 minutes and then cooled to room temperature. Next, 10 g ammoniumhydroxide was added and the contents of the flask was filtered to removeany coagulum. The resulting dispersion containing the polymer particleshad a solids content of 35.5 weight %, an average particle diameter of118 nm, and a pH of 9.5.

Example 2.12

To the flask was added 800 g deionized water and 3.0 g concentratedsulfuric acid. The contents of the flask was heated to a temperature of85° C. under a nitrogen atmosphere. A mixture of 3.0 g surfactant-Ahaving in 10 g deionized water was added to the flask followed by theaddition of ME-1, which was prepared by mixing 12 g deionized water, 1.0g of surfactant-A, 8.0 g butyl acrylate, and 28.0 g methyl methacrylate.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for a period of 10 minutes to allow polymerization of theadded monomers. After 10 minutes, ME-2, which contained 128 g deionizedwater, 12.8 g surfactant-A, 105.6 g butyl acrylate, 356.4 g methylmethacrylate, and 18.0 g purified phosphoethyl methacrylate, was addedto the flask at a rate of 7.5 g/minute at a temperature of 85° C. Aftercomplete addition of the ME-2, a solution of 4.0 g ammonium hydroxideand 10 g deionized water was added to the flask. Next, ME-3, whichcontained 32.0 g deionized water, 3.2 g surfactant-A, 28.8 g butylacrylate, and 91.2 g methyl methacrylate, was added to the flask at arate of 12.5 g/minute. Upon complete addition of the ME-3, the contentsof the flask was maintained at a temperature of 85° C. for a period of15 minutes and then cooled to room temperature. Next, 10 g ammoniumhydroxide was added and the contents of the flask was filtered to removeany coagulum. The resulting dispersion containing the polymer particleshad a solids content of 35.4 weight %, an average particle diameter of118 nm, and a pH of 9.4.

Example 2.13

To the flask was added 800 g deionized water and 3.0 g concentratedhydrochloric acid. The contents of the flask was heated to a temperatureof 85° C. under a nitrogen atmosphere. A mixture of 3.0 g surfactant-Ain 10 g deionized water was added to the flask followed by the additionof ME-1, which was prepared by mixing 12 g deionized water, 1.0 g ofsurfactant-A, 8.0 g butyl acrylate, and 28.0 g methyl methacrylate.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for a period of 10 minutes to allow polymerization of theadded monomers. After 10 minutes, ME-2, which contained 160 g deionizedwater, 16.0 g surfactant-A, 124.0 g butyl acrylate, 422.0 g methylmethacrylate, and 18.0 g purified phosphoethyl methacrylate, was addedto the flask at a rate of 7.5 g/minute at a temperature of 85° C. Aftercomplete addition of the ME-2, the contents of the flask was maintainedat a temperature of 85° C. for a period of 15 minutes and then cooled toroom temperature. Next, 16 g ammonium hydroxide was added and thecontents of the flask was filtered to remove any coagulum. The resultingdispersion containing the polymer particles had a solids content of 35.3weight %, an average particle diameter of 128 nm, and a pH of 9.0.

Example 2.14

To the flask was added 800 g deionized water and 3.0 g concentratedsulfuric acid. The contents of the flask was heated to a temperature of85° C. under a nitrogen atmosphere. A mixture of 3.0 g surfactant-A in10 g deionized water was added to the flask followed by the addition ofME-1, which was prepared by mixing 12 g deionized water, 1.0 g ofsurfactant-A, 8.0 g butyl acrylate, and 28.0 g methyl methacrylate.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for a period of 10 minutes to allow polymerization of theadded monomers. After 10 minutes, ME-2, which contained 80 g deionizedwater, 8.0 g surfactant-A, 66.0 g butyl acrylate, 222.0 g methylmethacrylate, and 6.0 g purified phosphoethyl methacrylate, was added tothe flask at a rate of 7.5 g/minute at a temperature of 85° C. Aftercomplete addition of the ME-2, a solution of 4.0 g ammonium hydroxide in10 g deionized water was added to the flask. Next, ME-3, which contained80 g deionized water, 8.0 g surfactant-A, 72.0 g butyl acrylate, and228.0 g methyl methacrylate, was added to the flask at a rate of 12.5g/minute. Upon complete addition of the ME-3, the contents of the flaskwas maintained at a temperature of 85° C. for a period of 15 minutes andthen cooled to room temperature. Next, 12 g ammonium hydroxide was addedand the contents of the flask was filtered to remove any coagulum. Theresulting dispersion containing the polymer particles had a solidscontent of 35.7 weight %, an average particle diameter of 128 nm, and apH of 9.5.

Example 2.15

To the flask was added 800 g deionized water and 3.0 g concentratedsulfuric acid. The contents of the flask was heated to a temperature of85° C. under a nitrogen atmosphere. A mixture of 3.0 g surfactant-A in10 g deionized water was added to the flask followed by the addition ofME-1, which was prepared by mixing 12 g deionized water, 1.0 g ofsurfactant-A, 8.0 g butyl acrylate, and 28.0 g methyl methacrylate.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for a period of 10 minutes to allow polymerization of theadded monomers. After 10 minutes, ME-2, which contained 80 g deionizedwater, 8.0 g surfactant-A, 27.0 g butyl acrylate, 255.0 g styrene, and18.0 g purified phosphoethyl methacrylate, was added to the flask at arate of 7.5 g/minute at a temperature of 85° C. After complete additionof the ME-2, a solution of 4.0 g ammonium hydroxide in 10 g deionizedwater was added to the flask. Next, ME-3, which contained 80 g deionizedwater, 8.0 g surfactant-A, 72.0 g butyl acrylate, and 228.0 g methylmethacrylate, was added to the flask at a rate of 12.5 g/minute. Uponcomplete addition of the ME-3, the contents of the flask was maintainedat a temperature of 85° C. for a period of 15 minutes and then cooled toroom temperature. Next, 10 g ammonium hydroxide was added and thecontents of the flask was filtered to remove any coagulum. The resultingdispersion containing the polymer particles had a solids content of 35.5weight %, an average particle diameter of 125 nm, and a pH of 9.0.

Example 2.16

To the flask was added 800 g deionized water and 0.7 g concentratedsulfuric acid. The contents of the flask was heated to a temperature of85° C. under a nitrogen atmosphere. A mixture of 3.0 g surfactant-A in10 g deionized water was added to the flask followed by the addition ofME-1, which was prepared by mixing 12 g deionized water, 1.0 g ofsurfactant-A, 8.0 g butyl acrylate, and 28.0 g methyl methacrylate.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for a period of 10 minutes to allow polymerization of theadded monomers. After 10 minutes, ME-2, which contained 80 g deionizedwater, 8.0 g surfactant-A, 66.0 g butyl acrylate, 216.0 g methylmethacrylate, 18.0 g purified phosphoethyl methacrylate, and 2.5 gconcentrated sulfuric acid, was added to the flask at a rate of 7.5g/minute at a temperature of 85° C. After complete addition of the ME-2,a solution of 4.0 g ammonium hydroxide in 10 g deionized water was addedto the flask. Next, ME-3, which contained 80 g deionized water, 8.0 gsurfactant-A, 72.0 g butyl acrylate, and 228.0 g styrene was added tothe flask at a rate of 12.5 g/minute. Upon complete addition of theME-3, the contents of the flask was maintained at a temperature of 85°C. for a period of 15 minutes and then cooled to room temperature. Next,10 g ammonium hydroxide was added and the contents of the flask wasfiltered to remove any coagulum. The resulting dispersion containing thepolymer particles had a solids content of 36.8 weight %, an averageparticle diameter of 114 nm, and a pH of 9.4.

Example 2.17

To the flask was added 800 g deionized water and 3.0 g concentratedsulfuric acid. The contents of the flask was heated to a temperature of85° C. under a nitrogen atmosphere. A mixture of 3.0 g surfactant-A in10 g deionized water was added to the flask followed by the addition ofME-1, which was prepared by mixing 12 g deionized water, 1.0 g ofsurfactant-A, 8.0 g butyl acrylate, and 28.0 g methyl methacrylate.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for a period of 10 minutes to allow polymerization of theadded monomers. After 10 minutes, ME-2, which contained 80 g deionizedwater, 8.0 g surfactant-A, 66.0 g butyl acrylate, 207.6 g methylmethacrylate, and 26.4 g phosphorylated caprolactone2-(methacryloxyloxy)ethyl ester, was added to the flask at a rate of 7.5g/minute at a temperature of 85° C. After complete addition of the ME-2,a solution of 4.0 g ammonium hydroxide in 10 g deionized water was addedto the flask. Next, ME-3, which contained 80 g deionized water, 8.0 gsurfactant-A, 72.0 g butyl acrylate, and 228.0 g methyl methacrylate,was added to the flask at a rate of 12.5 g/minute. Upon completeaddition of the ME-3, the contents of the flask was maintained at atemperature of 85° C. for a period of 15 minutes and then cooled to roomtemperature. Next, 10 g ammonium hydroxide was added and the contents ofthe flask was filtered to remove any coagulum. The resulting dispersioncontaining the polymer particles had a solids content of 35.2 weight %,an average particle diameter of 118 nm, and a pH of 7.5.

Example 2.18

To the flask was added 800 g deionized water and 3.0 g concentratedsulfuric acid. The contents of the flask was heated to a temperature of85° C. under a nitrogen atmosphere. A mixture of 3.0 g surfactant-A in10 g deionized water was added to the flask followed by the addition ofME-1, which was prepared by mixing 12 g deionized water, 1.0 g ofsurfactant-A, 8.0 g butyl acrylate, and 28.0 g methyl methacrylate.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for a period of 10 minutes to allow polymerization of theadded monomers. After 10 minutes, ME-2, which contained 80 g deionizedwater, 8.0 g surfactant-A, 66.0 g butyl acrylate, 213.9 g methylmethacrylate, and 20.1 g phosphorylated hydroxybutyl methacrylate, wasadded to the flask at a rate of 7.5 g/minute at a temperature of 85° C.After complete addition of the ME-2, a solution of 4.0 g ammoniumhydroxide in 10 g deionized water was added to the flask. Next, ME-3,which contained 80 g deionized water, 8.0 g surfactant-A, 72.0 g butylacrylate, and 228.0 g methyl methacrylate, was added to the flask at arate of 12.5 g/minute. Upon complete addition of the ME-3, the contentsof the flask was maintained at a temperature of 85° C. for a period of15 minutes and then cooled to room temperature. Next, 10 g ammoniumhydroxide was added and the contents of the flask was filtered to removeany coagulum. The resulting dispersion containing the polymer particleshad a solids content of 35.6 weight %, an average particle diameter of131 nm, and a pH of 8.0.

Example 2.19

To the flask was added 800 g deionized water and 3.0 g concentratedsulfuric acid. The contents of the flask was heated to a temperature of85° C. under a nitrogen atmosphere. A mixture of 3.0 g surfactant-A in10 g deionized water was added to the flask followed by the addition ofME-1, which was prepared by mixing 12 g deionized water, 1.0 g ofsurfactant-A, 8.0 g butyl acrylate, and 28.0 g methyl methacrylate.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for a period of 10 minutes to allow polymerization of theadded monomers. After 10 minutes, ME-2, which contained 80 g deionizedwater, 8.0 g surfactant-A, 66.0 g butyl acrylate, 207.0 g methylmethacrylate, and 27.0 g mono-phosphonoethyl methacrylate, was added tothe flask at a rate of 7.5 g/minute at a temperature of 85° C. Aftercomplete addition of the ME-2, a solution of 4.0 g ammonium hydroxide in10 g deionized water was added to the flask. Next, ME-3, which contained80 g deionized water, 8.0 g surfactant-A, 72.0 g butyl acrylate, and228.0 g methyl methacrylate, was added to the flask at a rate of 12.5g/minute. Upon complete addition of the ME-3, the contents of the flaskwas maintained at a temperature of 85° C. for a period of 15 minutes andthen cooled to room temperature. Next, 10 g ammonium hydroxide was addedand the contents of the flask was filtered to remove any coagulum. Theresulting dispersion containing the polymer particles had a solidscontent of 34.1 weight %, an average particle diameter of 116 nm, and apH of 8.7.

Example 2.20

To the flask was added 800 g deionized water and 3.0 g concentratedsulfuric acid. The contents of the flask was heated to a temperature of85° C. under a nitrogen atmosphere. A mixture of 3.0 g surfactant-A in10 g deionized water was added to the flask followed by the addition ofME-1, which was prepared by mixing 12 g deionized water, 1.0 g ofsurfactant-A, 8.0 g butyl acrylate, and 28.0 g methyl methacrylate.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for a period of 10 minutes to polymerize the addedmonomers. After 10 minutes, ME-2, which contained 80 g deionized water,8.0 g surfactant-A, 66.0 g butyl acrylate, 213.0 g methyl methacrylate,3.0 g allyl methacrylate, and 18.0 g purified phosphoethyl methacrylate,was added to the flask at a rate of 7.5 g/minute at a temperature of 85°C. After complete addition of the ME-2, a solution of 4.0 g ammoniumhydroxide in 10 g deionized water was added to the flask. Next, ME-3,which contained 80 g deionized water, 8.0 g surfactant-A, 72.0 g butylacrylate, and 228.0 g styrene, was added to the flask at a rate of 12.5g/minute. Upon complete addition of the ME-3, the contents of the flaskwas maintained at a temperature of 85° C. for a period of 15 minutes andthen cooled to room temperature. Next, 10 g ammonium hydroxide was addedand the contents of the flask was filtered to remove any coagulum. Theresulting dispersion containing the polymer particles had a solidscontent of 35.5 weight %, an average particle diameter of 123 nm, and apH of 8.9.

Example 2.21

To the flask was added 800 g deionized water and 3.0 g concentratedsulfuric acid. The contents of the flask was heated to a temperature of85° C. under a nitrogen atmosphere. A mixture of 3.0 g surfactant-A in10 g deionized water was added to the flask followed by the addition ofME-1, which was prepared by mixing 12 g deionized water, 1.0 g ofsurfactant-A, 8.0 g butyl acrylate, and 28.0 g methyl methacrylate.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for a period of 10 minutes to allow polymerization of theadded monomers. After 10 minutes, ME-2, which contained 40 g deionizedwater, 4.0 g surfactant-A, 33.0 g butyl acrylate, 104.9 g methylmethacrylate, 1.5 g allyl methacrylate, and 10.6 g unpurifiedphosphoethyl methacrylate, was added to the flask at a rate of 7.5g/minute at a temperature of 85° C. After complete addition of the ME-2,a solution of 4.0 g ammonium hydroxide in 10 g deionized water was addedto the flask. Next, ME-3, which contained 120 g deionized water, 12.0 gsurfactant-A, 108.0 g butyl acrylate, and 342.0 g styrene, was added tothe flask at a rate of 12.5 g/minute. Upon complete addition of theME-3, the contents of the flask was maintained at a temperature of 85°C. for a period of 15 minutes and then cooled to room temperature. Next,10 g ammonium hydroxide was added and the contents of the flask wasfiltered to remove any coagulum. The resulting dispersion containing thepolymer particles had a solids content of 34.6 weight %, an averageparticle diameter of 120 nm, and a pH of 8.8.

Comparative Examples

Comparative aqueous dispersions containing polymer particles havingphosphorus acid groups were prepared by aqueous emulsion polymerizationof phosphorus acid monomer at a pH value of greater than 2. Thecomparative dispersions were prepared in the same reactor used toprepare the aqueous dispersions of Example 2.1 to 2.21.

Comparative Example C.1

To the flask was added 1800 g deionized water, which was then heated toa temperature of 80° C. under a nitrogen atmosphere. A mixture of 11.8 gsodium lauryl sulfate (SLS) in 10 g deionized water was added to theflask followed by a mixture of 6.0 g sodium persulfate in 60 g deionizedwater. After the addition of the sodium persulfate solution, ME-1, whichcontained 520.0 g deionized water, 53.6 g SLS, 330 g butyl acrylate,1110.0 g methyl methacrylate, 15.0 g acrylic acid, and 45.0 g unpurifiedphosphoethyl methacrylate, was added to the flask at a rate of 18.3g/minute at a temperature of 80° C. After complete addition of the ME-1,the contents of the flask was maintained at a temperature of 85° C. fora period of 15 minutes and then cooled to room temperature. Next, 25 gammonium hydroxide was added and the contents of the flask was filteredto remove any coagulum. The resulting comparative dispersion, containingpolymer particles, had a solids content of 37.1 weight %, an averageparticle diameter of 73 nm, and a pH of 8.1.

Comparative Example C.2

To the flask was added 800 g deionized water, which was then heated to atemperature of 85° C. under a nitrogen atmosphere. A mixture of 3.0 gsurfactant-A in 10 g deionized water was added to the flask followed bythe addition of ME-1, which contained 12 g deionized water, 1.0 g ofsurfactant-A, 7.9 g butyl acrylate, 27.7 g methyl methacrylate, and 0.4g methacrylic acid. Following addition of the ME-1, a mixture of 2.4 gsodium persulfate in 20 g deionized water was added to the flask and thecontents of the flask was held for 10 minutes to allow thepolymerization of the monomers. After 10 minutes, ME-2, which contained170 g deionized water, 16.0 g of surfactant-A, 124.1 g butyl acrylate,416.3 g methyl methacrylate, 5.6 g acrylic acid, and 18.0 g purifiedphosphoethyl methacrylate, was added to the flask at a rate of 7.5g/minute at a temperature of 85° C. After the completion of ME-2, thecontents of the flask was maintained at a temperature of 85° C. for aperiod of 15 minutes and then cooled to room temperature. Next, 11 gammonium hydroxide was added and the contents of the flask was filteredto remove any coagulum. The resulting comparative dispersion, containingpolymer particles, had a solids content of 34.9 weight %, an averageparticle diameter of 110 nm, and a pH of 8.4. The resulting comparativeaqueous polymer dispersion contained a ratio of equivalents of secondphosphorus acid groups to equivalents of first phosphorus acid groupsequal to 2.45.

Comparative Example C.3

To the flask was added 800 g deionized water, which was then heated to atemperature of 85° C. under a nitrogen atmosphere. A mixture of 3.0 gsurfactant-A in 10 g deionized water was added to the flask followed bythe addition of ME-1, which contained 12 g deionized water, 1.0 g ofsurfactant-A, 8.0 g butyl acrylate, and 28.0 g methyl methacrylate.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for 10 minutes to allow polymerization of the monomers.After 10 minutes, ME-2, which contained 80 g deionized water, 8.0 gsurfactant-A, 96.0 g ethyl acrylate, 186.0 g methyl methacrylate, and18.0 g purified phosphoethyl methacrylate, was added to the flask at arate of 7.5 g/minute at a temperature of 85° C. After complete additionof the ME-2, ME-3, which contained 80 g deionized water, 8.0 gsurfactant-A, 72.0 g butyl acrylate, and 228.0 g methyl methacrylate,was added to the flask at a rate of 12.5 g/minute. Upon completeaddition of the ME-3, the reaction was maintained at a temperature of85° C. for a period of 15 minutes and then cooled to room temperature.Next, 12 g ammonium hydroxide were added and the contents of the flaskwas filtered to remove any coagulum. The resulting comparativedispersion, containing polymer particles, had a solids content of 36.5weight %, an average particle diameter of 112 nm, and a pH of 9.9.

Comparative Example C.4

To the flask was added 800 g deionized water, which was then heated to atemperature of 85° C. under a nitrogen atmosphere. A mixture of 3.0 gsurfactant-A in 10 g deionized water was added to the flask followed bythe addition of ME-1, which contained 12 g deionized water, 1.0 g ofsurfactant-A, 8.0 g butyl acrylate, and 28.0 g methyl methacrylate.Following addition of the ME-1, a mixture of 2.4 g sodium persulfate in20 g deionized water was added to the flask and the contents of theflask was held for 10 minutes to allow polymerization of the monomers.After 10 minutes, ME-2, which contained 170 g deionized water, 16.0 gsurfactant-A, 124.0 g butyl acrylate, 422.0 g methyl methacrylate, and18.0 g purified phosphoethyl methacrylate, was added to the flask at arate of 7.5 g/minute at a temperature of 85° C. After complete additionof the ME-2, the contents of the flask was maintained at a temperatureof 85° C. for a period of 15 minutes and then cooled to roomtemperature. Next, 16 g ammonium hydroxide was added and the contents ofthe flask was filtered to remove any coagulum. The resulting comparativedispersion containing polymer particles had a solids content of 34.8weight %, an average particle size of 106 nm, and a pH of 10.0.

In Table 2.1, the pH values for the polymerization of the phosphorusacid monomer are listed. The pH values were measured prior to and afterthe addition and polymerization of the monomer emulsion containing thephosphorus acid monomer. The table also lists the type of phosphorusacid monomer and indicates if the phosphorus acid monomer was purifiedto remove free phosphoric acid. TABLE 2.1 Process pH values forPolymerization of Phosphorus Acid Monomer Process pH (start/finish)Phosphorus Acid Monomer Example 2.1 1.5/1.5 purified PEM Example 2.21.7/1.6 purified PEM Example 2.3 1.5/1.5 purified PEM Example 2.41.5/1.5 purified PEM Example 2.5 1.5/1.5 purified PEM Example 2.6 1/1purified PEM Example 2.7 1/1 purified PEM Example 2.8 1/1 purified PEMExample 2.9 1/1 unpurified PEM Example 2.10 1/1 purified PEM Example2.11 1/1 purified PEM Example 2.12 1/1 purified PEM Example 2.13 0.8/0.8purified PEM Example 2.14 1/1 purified PEM Example 2.15 1/1 purified PEMExample 2.16 1.5/1   purified PEM Example 2.17 1/1 phosphorylatedcaprolactone 2-(methacryloyloxy)ethyl ester Example 2.18 1/1phosphorylated hydroxybutyl methacrylate Example 2.19 1/1mono-phosphonoethyl methacrylate Example 2.20 1/1 purified PEM Example2.21 1/1 unpurified PEM Comparative C.1 7.5/2.2 unpurified PEMComparative C.2 7.5/2.2 purified PEM Comparative C.3 7.5/2.1 purifiedPEM Comparative C.4 7.5/2.2 purified PEMPEM = phosphoethyl methacrylate

Preparation of Composite Particles with Adsorbed Polymer ParticlesPreparation of Pigment Particle Dispersion

A mixture of 133.0 g of water, 8.9 g of Tamol™ 731A dispersant (Tamol isa trademark of Rohm and Haas Company), 10 g of Colloid™ 643 dispersant(Colloid is a trademark of Allied Colloids Limited Company, UK), and 5 gof 28% NH₃ were placed in grind pot. The contents of the grind pot weremixed on a Premier Mill dispersator equipped with a disk blade. To thegrind pot, 553.5 g of TiPure™ R-706 titanium dioxide (TiPure is atrademark of E.I. DuPont de Nemours and Company) was added to the potand ground at 2000 rpm for 20 min to prepare a titanium dioxide particledispersion.

Example 2.1a Aqueous Composition Containing Composite Particles

An aqueous composition containing composite particles was prepared byadding dropwise and with mixing 16.8 g of the titanium dioxide particledispersion prepared above and 0.4 g of 28% ammonium hydroxide to 23.2 gof the aqueous dispersion of Example 2.1. The resulting aqueouscomposition was placed on a roller for at least 12 hours prior toformulation into a coating composition. The resulting aqueouscomposition had a solids level of 51.3 weight % and a pH greater than 8.The composite particles contained 63.1 weight % titanium dioxideparticles and 36.9 weight % polymer particles.

Example 2.2a Aqueous Composition Containing Composite Particles

An aqueous composition containing composite particles was prepared byadding dropwise and with mixing 40 g of the titanium dioxide particledispersion prepared above to a mixture of 53.9 g of the aqueousdispersion of Example 2.2 and 2.8 g water. The resulting aqueouscomposition was placed on a roller for at least 12 hours prior toformulation into a coating composition.

Example 2.4a Aqueous Composition Containing Composite Particles

An aqueous composition containing composite particles was prepared byadding dropwise and with mixing 38 g of the titanium dioxide particledispersion prepared above to a mixture of 48.8 g of the aqueousdispersion of Example 2.4 and 3.8 g water. The resulting aqueouscomposition was placed on a roller for at least 12 hours prior toformulation into a coating composition.

Example 2.5a Aqueous Composition Containing Composite Particles

An aqueous composition containing composite particles was prepared byadding dropwise and with mixing 38 g of the titanium dioxide particledispersion prepared above to a mixture of 49.2 g of the aqueousdispersion of Example 2.5 and 2.4 g water. The resulting aqueouscomposition was placed on a roller for at least 12 hours prior toformulation into a coating composition.

Example 2.8a Aqueous Composition Containing Composite Particles

An aqueous composition containing composite particles was prepared byadding dropwise and with mixing 40 g of the titanium dioxide particledispersion prepared above to a mixture of 51.4 g of the aqueousdispersion of Example 2.8 and 5.3 g water. The resulting aqueouscomposition was placed on a roller for at least 12 hours prior toformulation into a coating composition.

Comparative Example C.1a Comparative Aqueous Composition ContainingComparative Composite Particles

A comparative aqueous composition was prepared containing comparativecomposite particles using the comparative aqueous dispersion ofComparative Example C.1. These comparative polymer particles wereprepared with a polymerization process at a pH above 2. The comparativeaqueous composition was prepared by adding dropwise and with mixing 16.8g of the titanium dioxide dispersion prepared above and 0.40 g of 28%ammonium hydroxide to 23.33 g of the comparative aqueous dispersion ofComparative Example C.1. The resulting comparative aqueous compositioncontaining the comparative composite particles was placed on a rollerfor at least 12 hours prior to formulation into a comparative coatingcomposition. The comparative composite particle composition ofComparative C.1a had a solids level of 53.7 weight % and a pH above 8.The comparative composite particles contained 60.2 weight % titaniumdioxide particles and 39.8 weight % comparative polymer particles.

Preparation of Pigment Particle Dispersion

A mixture of 133.0 g of water, 8.9 g Tamol™ 731A dispersant (Tamol is atrademark of Rohm and Haas Company), 10 g Colloid™ 643 dispersant, and 5g of 28% NH₃ were placed in grind pot. The contents of the grind potwere mixed on a Premier Mill dispersator equipped with a disk blade. Tothe grind pot, 553.5 g of TiPure™ R-706 titanium dioxide was added andground at 2000 rpm for 20 min to prepare a titanium dioxide particledispersion.

Comparative Example C.2a Comparative Aqueous Composition ContainingComparative Composite Particles

A comparative aqueous composition containing composite particles wasprepared by adding dropwise and with mixing 40.0 g of the titaniumdioxide dispersion prepared above to a mixture of 53.7 g of thecomparative aqueous dispersion of Comparative Example C.2 and 2.9 gwater. The resulting comparative aqueous composition was placed on aroller for at least 12 hours prior to formulation into a coatingcomposition.

Comparative Example C.3a Comparative Aqueous Composition ContainingComparative Composite Particles

A comparative aqueous composition containing composite particles wasprepared by adding dropwise and with mixing 40.0 g of the titaniumdioxide dispersion prepared above to a mixture of 51.2 g of thecomparative aqueous dispersion of Comparative Example C.3 and 5.4 gwater. The resulting comparative aqueous composition was placed on aroller for at least 12 hours prior to formulation into a coatingcomposition.

Comparative Example C.4a Comparative Aqueous Composition ContainingComparative Composite Particles

A comparative aqueous composition containing composite particles wasprepared by adding dropwise and with mixing 38.0 g of the titaniumdioxide dispersion prepared above to a mixture of 49.9 g of thecomparative aqueous dispersion of Comparative Example C.4 and 2.7 gwater. The resulting comparative aqueous composition was placed on aroller for at least 12 hours prior to formulation into a coatingcomposition.

Comparative Example C.5 Comparative Dispersion Containing TitaniumDioxide Particles and Comparative Polymer Particles

A comparative dispersion was prepared containing titanium dioxideparticles and comparative polymer particles. The comparative dispersiondid not contain the composite particles as the comparative polymerparticles were not adsorbed or covalently bonded to the titanium dioxideparticles.

Preparation of Pigment Particle Dispersion

A mixture of 133.0 g of water, 8.9 g Tamol™ 731A dispersant (Tamol is atrademark of Rohm and Haas Company), 10 g Colloid™ 643 dispersant, and 5g of 28% NH₃ were placed in grind pot. The contents of the grind potwere mixed on a Premier Mill dispersator equipped with a disk blade. Tothe grind pot, 553.5 g of TiPure™ R-706 titanium dioxide was added andground at 2000 rpm for 20 min to prepare a titanium dioxide particledispersion.

Preparation of Comparative Dispersion

A comparative dispersion was prepared by adding dropwise and with mixing140 g of the titanium dioxide dispersion prepared above to 155.4 g ofRhoplex™ SG-20 polymer (Rohm and Haas Company). Rhoplex™ SG-20 polymeris supplied at 45.5 weight % solids and has an average particle diameterof 150 nm.

Example 3 Preparation of Coating Compositions and Comparative CoatingCompositions

Two coating compositions containing the composite particles of Example1.1a were prepared at 2 and 30 pigment volume concentration (PVC) byadding the ingredients in the order listed in Table 3.1. TABLE 3.1Coating Compositions at 2 PVC and 30 PVC Example 3.1 Example 3.2 Example1.1a 9.55 g 143.29 g  Isocyanate Functional Polymer 107.46 g  — ParticleDispersion of Example 1.1 Texanol ™ coalescent 3.33 g 2.38 g Natrosol ™250HR thickener (2.5% 12.24 g  12.24 g  aqueous solution) Water — 16.77g  Ammonium hydroxide (28%) 0.49 g 0.49 g Supronil ™ HK Black Liquid0.49 g 0.49 g PVC 2 30

(Texanol is a trademark of Eastman Chemical Corp, Kingsport, Tenn.).These two coating compositions, Examples 3.1-3.2, were then blended invarious ratios, as listed in Table 3.2, to prepare coating compositionsat several other pigment volume ratios. TABLE 3.2 Coating CompositionsFrom Blends of Example 3.1 and 3.2 Example 3.3 Example 3.4 Example 3.5Example 3.6 Example 3.1 36.52 g 33.59 g 21.91 g  7.30 g Example 3.2 5.36 g  8.93 g 23.22 g 41.07 g PVC 5 7 15 25

A coating composition was prepared containing the composite particles ofExample 1.2a at 15 PVC. First, a master formulation was prepared bycombining 416 g of Rhoplex™ AC-261 polymer dispersion, 1.92 g Supronil™HK Black Liquid, 24 g Texanol™ coalescent, 64.8 g water, and 50 g of a2.5 weight % aqueous solution of Natrosol™ 250HR thickener (HerculesCorp., Wilmington, Del.) while stirring on a bench top stirrer. Next,the composite particle dispersion of Example 1.2a was combined with themaster formulation to prepare the coating composition of Example 3.7. Aclear coating was also prepared from the master formulation, containingthe ingredients listed in Table 3.3. TABLE 3.3 Coating Composition at 15PVC and Clear Coating Composition Clear Coating Composition Example 3.7Example 1.2a — 36.05 g Rhoplex ™ AC-261 45.27 g — polymer dispersionMaster formulation  69.0 g 34.81 g PVC 0 15

The coating composition of Example 3.7 and the clear coating compositionwere then blended in various ratios, as listed in Table 3.4, to preparecoating compositions at several other pigment volume ratios. TABLE 3.4Coating Compositions From Blends of Example 3.1 and 3.2 Example ExampleExample Example 3.8 3.9 3.10 3.11 Clear Coating 8.15 g 5.93 g 3.70 g 1.48 g Composition Example 3.7 3.64 g 6.36 g 9.09 g 11.81 g PVC 4 7 1013

A coating composition was prepared containing the composite particles ofExample 2.1a at 16 PVC. First, a master formulation was prepared bycombining 564.0 g of Rhoplex™ AC-261 polymer dispersion, 2.9 g Supronil™HK Black Liquid, 35.0 g Texanol™ coalescent, 102.5 g water, and 67.7 gNatrosol 250HR thickener (3% solids in water) while stirring on a benchtop stirrer. Next, the composite particle dispersion of Example 2 wascombined with the master formulation to prepare the coating compositionof Example 3.12. A clear coating was also prepared from the masterformulation, containing the ingredients listed in Table 3.5. TABLE 3.5Coating Composition at 16 PVC Example 3.12 Example 2.1a 40.46 g Masterformulation 32.17 g PVC 16

Coating compositions were prepared at various pigment volumeconcentrations by blending the composition of Example 3.12 and themaster formulation, as listed in Table 3.6. TABLE 3.6 CoatingCompositions From Blends of Example 3.12 and Master Formulation ExampleExample Example Example Example 3.13 3.14 3.15 3.16 3.17 Master 57.85 g42.21 g 34.24 g 27.45 g 13.35 g Formulation Example 22.15 g 37.80 g45.77 g 52.55 g 66.66 g 3.12 PVC 4 7 8.6 10 13

Comparative coating compositions were prepared at 2 and 30 pigmentvolume concentration (PVC) by adding the ingredients in the order listedin Table 3.7. TABLE 3.7 Comparative Coating Composition ComparativeComparative Example A.1 Example A.2 Comparative Example C.1a 8.82 g132.27 g  Rhoplex ™ SG-20 polymer dispersion 92.77 g  — Texanol ™coalescent 3.33 g 2.38 g Natrosol ™ 250HR thickener (2.5% 12.24 g  12.24g  aqueous solution) Water 24.73 g  27.79 g  Ammonium hydroxide (28%)0.49 g 0.49 g Supronil ™ HK Black Liquid 0.49 g 0.49 g PVC 2 30

The comparative coating compositions of Comparative Examples A.1 andA.2, were then blended in various ratios, as listed in Table 3.8, toprepare coating compositions at several other pigment volume ratios.TABLE 3.8 Comparative Coating Compositions From Blends of ComparativeExamples A.1 and A.2 Comparative Comparative Comparative ComparativeExample A.3 Example A.4 Example A.5 Example A.6 Comparative 36.31 g33.40 g 21.78 g  7.26 g Example A.1 Comparative  5.36 g  8.93 g 23.22 g41.07 g Example A.2 PVC 5 7 15 25

A second comparative coating composition was prepared containing thecomparative composite particles of Comparative Example C.2a at 16 PVC.First, a master formulation was prepared by combining 564.0 g ofRhoplex™ AC-261 polymer dispersion, 35.0 g Texanol™ coalescent, 102.5 gwater, 2.9 g Supronil™ HK Black Liquid, and 67.7 g Natrosol 250HRthickener (3% solids in water) while stirring on a bench top stirrer.Next, the composite particle dispersion of Comparative Example C.2a wascombined with the master formulation to prepare the coating compositionof Comparative Example A.7. TABLE 3.9 Comparative Coating Composition at15 PVC Comparative Example A.7 Comparative Example C.2a 40.46 g Masterformulation 32.17 g PVC 16

The comparative coating composition of Comparative Example A.7 and themaster formulation were then blended in various ratios, as listed inTable 3.10, to provide coating compositions at several other pigmentvolume ratios. TABLE 3.10 Comparative Coating Compositions From Blendsof Comparative Example A.7 and Master Formulation ComparativeComparative Comparative Comparative Example Example A.8 Example A.9Example A.10 A.11 Master 57.9 g 42.2 g 27.5 g 13.4 g FormulationComparative 22.2 g 37.8 g 52.6 g 66.7 g Example A.7 PVC 4 7 10 13

Example 3.18 and Comparative Example A.12

A master formulation was prepared by combining 329.8 g of Rhoplex™AC-261 polymer dispersion, 1.7 g Supronil™ HK Black Liquid, 27.7 gTexanol™ coalescent, 58.2 g water, and 42.6 g Natrosol 250HR thickener(2.5% solids in water) while stirring on a bench top stirrer. Next, theaqueous composition of Example 2.8a was combined with the masterformulation to prepare the coating composition of Example 3.18. Acomparative coating composition was prepared from the comparativeaqueous composition of Comparative Example C.3a. TABLE 3.5 Preparationof Coating Composition and Comparative Coating Composition ExampleComparative 3.18 Example A.12 Master Formulation 35.2 g 35.2 g Example2.8a 45.0 g Comparative Example C.3a 45.0 g PVC 16 16

Example 3.19 and Comparative Example A.13

A master formulation was prepared by combining 659.6 g of Rhoplex™AC-261 polymer dispersion, 3.42 g Supronil™ HK Black Liquid, 41.55 gTexanol™ coalescent, 116.4 g water, and 85.2 g Natrosol 250HR thickener(2.5% solids in water) while stirring on a bench top stirrer. Next, theaqueous composition of Example 2.3 was combined with the masterformulation to prepare the coating composition of Example 3.19. Acomparative coating composition was prepared from the comparativeaqueous composition of Comparative A.13. TABLE 3.6 Preparation ofCoating Composition and Comparative Coating Composition Example 3.19Comparative Example A.13 Master Formulation 36.53 g 36.53 g Example 2.2a50.0 g Comparative Example C.2a 50.0 g PVC 16 16

Examples 3.20-3.21 and Comparative A.14

A master formulation was prepared by combining 372.7 g of Rhoplex™AC-261 polymer dispersion, 1.90 g Supronil™ HK Black Liquid, 23.15 gTexanol™ coalescent, 67.72 g water, and 44.72 g Natrosol 250HR thickener(2.5% solids in water) while stirring on a bench top stirrer. Next, theaqueous compositions of Example 2.4a and Example 2.5a were each combinedwith the master formulations to prepare the coating compositions ofExample 3.20 and Example 3.21, respectively. A comparative coatingcomposition was prepared from the comparative aqueous composition ofComparative C.4a. TABLE 3.7 Preparation of Coating Compositions andComparative Coating Composition Example Comparative Example 3.20 3.21Example A.14 Master Formulation 32.2 g 32.2 g 32.2 g Example 2.4a 40.0 gExample 2.5a 40.0 g Comparative Example C.4a 40.0 g PVC 16 16 16

Example 4 Preparation and Evaluation of Coated Samples

Preparation of Coated Samples:

Coated samples were prepared by applying a 76 micron (3 mil) thick wetfilm of the coating composition onto Opacity Charts (The Leneta Company,Form 3B) with a Bird blade (MED Industries) and allowing the wet film todry at 20° C. and 20% relative humidity for at least 12 hours.

Determination of Scattering Coefficients:

The Y-reflectance value of the coated sample was measured over the blackpart of the chart with a Pacific Scientific Colorguard colorimeter(Gardner Ineotec). The reported Y-reflectance value is an average ofthree measurements. Scattering coefficients were calculated using theequationS=2.578*Y/(1−Y)²,

where Y represents the Y-reflectance value and the value of 2.578 forthe constant coefficient was selected to provide a 2 PVC coating with ascattering coefficient of 1.000. Table 4.1 lists the Y-reflectancevalues and the calculated scattering coefficients for the coatingcompositions and the comparative coating compositions with PVC values inthe range of 2 to 30. TABLE 4.1 Y-Reflectance Values and ScatteringCoefficients for Coatings Prepared from Coating Compositions andComparative Coating Compositions Y-Re- Scattering flectance Co- CoatingComposition Value efficient PVC Comments Example 3.1 0.2310 1.000 2Example 1.1a Example 3.3 0.3720 2.432 5 Example 3.4 0.4315 3.441 7Example 3.5 0.5665 7.771 15 Example 3.6 0.6530 13.98 25 Example 3.20.6710 15.96 30 Example 3.8 0.4150 3.126 4 Example 1.2a Example 3.90.5080 5.410 7 Example 3.10 0.5668 7.786 10 Example 3.11 0.6030 9.863 13Example 3.7 0.6160 10.77 15 Example 3.13 0.398 1.098 4 Example 2.1aExample 3.14 0.491 1.895 7 Example 3.15 0.520 2.257 8.6 Example 3.160.547 2.666 10 Example 3.17 0.585 3.397 13 Example 3.12 0.611 4.038 16Comparative Example A.1 0.2300 1.000 2 Comparative C.1a ComparativeExample A.3 0.3790 2.533 5 Comparative Example A.4 0.4300 3.412 7Comparative Example A.5 0.5220 5.889 15 Comparative Example A.6 0.56407.648 25 Comparative Example A.2 0.5660 7.748 30 Comparative Example A.80.396 1.085 4 Comparative C.2a Comparative Example A.9 0.482 1.796 7Comparative Example A.10 0.532 2.429 10 Comparative Example A.11 0.5652.986 13 Comparative Example A.7 0.589 3.487 16

The hiding efficiencies provided by the titanium dioxide particles inthe coatings in Table 4.1 were determined by fitting the values for thescattering coefficients and the pigment volume concentration of thetitanium dioxide to the following equation:S=AV(1−BV ^(1/3))

where S represents the scattering coefficient, V represents the pigmentvolume concentration of the titanium dioxide, and A and B are constants.Values of B were determined for the coatings containing the compositeparticles of Example 1.1a, Example 1.2a, Example 2a, the comparativecomposite particles of Comparative Example C.2a, and the titaniumdioxide particles of Comparative Example C.5. TABLE 4.2 Values of B forCoatings Prepared from Coating Compositions and Comparative CoatingCompositions Coating Composition B Comments Examples 3.1-3.6 −0.07 ±0.06  composite particles of Example 1.1a Examples 3.7-3.11 0.099 ±0.035 composite particles of Example 1.2a Examples 3.12-3.17 0.08 ± 0.01composite particles of Example 2.1a Comparative 0.22 ± 0.01 titaniumdioxide particles of Examples A.1-A.6 Comparative Example C.1aComparative  0.17 ± 0.005 comparative composite Examples A.7-A.11particles of Comparative Example C.2a Literature value for 0.23 TiPure ™titanium titanium dioxide dioxide particle particlesThe results in Table 4.2 show that the coatings of this invention, asexemplified by Examples 3.1-3.17, have B values of less than or equal to0.15. This indicates that the titanium dioxide pigment particles inthese coatings have scattering coefficients with a linear orquasi-linear relationship to the pigment volume concentration of thetitanium dioxide particles contained in the coatings. In comparison, thecomparative coatings have significantly lower levels of hiding. The Bvalues for the titanium dioxide contained in the comparative coatingswere greater than 0.15. The coating with titanium dioxide particles thatwere not contained in composite particles, had the largest value for B,indicating significant crowding of the titanium dioxide particles andloss of hiding efficiency.

The Y-reflectance values were also measured for the coatings preparedfrom Examples 3.18-2.21 and Comparative Examples A.12-A.14. A differenceof 0.2 units or greater in the Y-reflectance values was visuallydiscernible and was considered to be significant.

The Y-values for coatings prepared from Example 3.18 and ComparativeExample A.12 were measured to be 67.2 and 65.8, respectively. Thepolymer particles contained in Example 3.18 and the comparative polymerparticles of Comparative Example A.12 had the same polymer composition.The polymer particles of Example 3.18 were prepared by the low pHprocess of this invention. The comparative polymer particles ofComparative Example A.12 were prepared by a polymerization process at apH above 2.

The Y-values for coatings prepared from Example 3.19 and ComparativeExample A.13 were measured to be 68.0 and 66.6, respectively. Thepolymer particles contained in Example 3.19 and the comparative polymerparticles of Comparative Example A.13 had the same polymer composition.The polymer particles contained in Example 3.19 were prepared by the lowpH process of this invention. The comparative polymer particlescontained in Comparative Example A.13 were prepared by a polymerizationprocess at a pH above 2.

The Y-values for coatings prepared from Example 3.20, Example 3.21, andComparative Example A.14 were measured to be 67.1, 67.0, and 66.3,respectively. The polymer particles contained in Example 3.20, Example3.21, and the comparative polymer particles of Comparative Example A.14had the same polymer composition. The polymer particles contained inExample 3.20 and Example 3.21 were prepared by the low pH process ofthis invention. The comparative polymer particles contained inComparative Example A.14 were prepared by a polymerization process at apH above 2.

The results show that the polymer particles prepared by a polymerizationprocess of this invention provided a coating with higher level of hidingthat a comparative coating containing polymer particles prepared by apolymerization process having a pH above 2.

1-5. (canceled)
 6. A composite particle comprising: a) a pigmentparticle; and b) a plurality of polymer particles, each one of saidpolymer particles comprising at least one reacted complementaryfunctional group forming a covalent bond with said pigment particle. 7.A composite particle comprising: a) a pigment particle; b) a firstplurality of polymer particles; and c) a second plurality of reactedcoupling agents, such that each one of said reacted coupling agents iscovalently bonded to said pigment particle and to a corresponding one ofsaid first plurality of polymer particles. 8-12. (canceled)
 13. Thecomposite particle of claim 6 wherein the first plurality of polymerparticles are on a surface of the pigment particle.
 14. The compositeparticle of claim 6 wherein the covalent bond comprises reacted couplingagents bonded to the pigment particle and to a corresponding polymerparticle.
 15. The composite particle of claim 6 wherein the pigmentparticle comprises an average particle diameter of up to 1 micron, asurface, and an index of refraction of at least 1.8.
 16. The compositeparticle of claim 6 wherein the at least one unreacted complementaryfunctional group comprises at least one of an aziridine, an epoxide, anda thiorane.
 17. The composite particle of claim 6 wherein the covalentbond is formed by a connecting bond, comprising the at least one reactedcomplementary functional group, represented by a structure:—C(X₁)H—C(X₂)H—Y—M— wherein: X₁ is —OH, —SH, or —NH and X₂ is —H; andalternatively X₂ is —OH, —SH, or —NH and X₁ is —H; Y is O or S; and M isan atom in the pigment particle and is selected from: Ti, Al, Zr, Si,Zn, Cr, Sn, Fe, C, and Pb.
 18. The composite particle of claim 7 whereinthe first plurality of polymer particles are on a surface of the pigmentparticle.
 19. The composite particle of claim 7 wherein the pigmentparticle comprises an average particle diameter of up to 1 micron, asurface, and an index of refraction of at least 1.8.
 20. The compositeparticle of claim 7 wherein the coupling agent covalently bonds to saidfirst plurality of polymer particles by at least one of an ester, amide,ether, urethane, thiol ether, amine, and ureido.
 21. The compositeparticle of claim 7 wherein each one of the second plurality of reactedcoupling agents are bonded to atoms at least one of on and at a surfaceof the pigment particle by bonds selected from ether bonds, thiol etherbonds, and siloxane ether bonds.
 22. The composite particle of claim 21wherein the atom comprises at least one of Ti, Al, Zr, Si, Zn, Cr, Sn,Fe, C, and Pb.
 23. The composite particle of claim 7 wherein each one ofthe second plurality of reacted coupling agents coupling agent comprisesa molecular weight of less than about 10,000.